Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.53   9.760%   $211.3209   $211.32   $211.30   $211.30  
  Purchase #2 $164.99   11.610%   $184.1453   $184.15   $184.15   $184.10  
  Purchase #3 $184.56   8.391%   $200.0464   $200.05   $200.05   $200.00  
  Purchase #4 $152.47   7.331%   $163.6476   $163.65   $163.65   $163.60  
  Purchase #5 $178.95   11.448%   $199.4362   $199.44   $199.45   $199.40  
  Purchase #6 $186.65   5.126%   $196.2177   $196.22   $196.20   $196.20  
  Purchase #7 $117.94   7.197%   $126.4281   $126.43   $126.45   $126.40  
  7 purchase totals = $1,178.09       $1,281.2422   $1,281.26   $1,281.25   $1,281.00