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 $204.34   3.576%   $211.6472   $211.65   $211.65   $211.60  
  Purchase #2 $114.53   9.713%   $125.6543   $125.65   $125.65   $125.70  
  Purchase #3 $179.76   11.190%   $199.8751   $199.88   $199.90   $199.90  
  Purchase #4 $78.73   7.184%   $84.386   $84.39   $84.40   $84.40  
  Purchase #5 $228.85   10.508%   $252.8976   $252.90   $252.90   $252.90  
  Purchase #6 $172.33   4.404%   $179.9194   $179.92   $179.90   $179.90  
  Purchase #7 $126.49   7.541%   $136.0286   $136.03   $136.05   $136.00  
  7 purchase totals = $1,105.03       $1,190.4082   $1,190.42   $1,190.45   $1,190.40