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 $191.41   8.709%   $208.0799   $208.08   $208.10   $208.10  
  Purchase #2 $249.67   9.344%   $272.9992   $273.00   $273.00   $273.00  
  Purchase #3 $157.43   4.365%   $164.3018   $164.30   $164.30   $164.30  
  Purchase #4 $145.54   7.647%   $156.6694   $156.67   $156.65   $156.70  
  Purchase #5 $142.68   9.743%   $156.5813   $156.58   $156.60   $156.60  
  Purchase #6 $207.65   6.144%   $220.408   $220.41   $220.40   $220.40  
  Purchase #7 $63.87   11.145%   $70.9883   $70.99   $71.00   $71.00  
  7 purchase totals = $1,158.25       $1,250.0279   $1,250.03   $1,250.05   $1,250.10