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 $116.68   7.233%   $125.1195   $125.12   $125.10   $125.10  
  Purchase #2 $108.98   11.795%   $121.8342   $121.83   $121.85   $121.80  
  Purchase #3 $234.34   6.428%   $249.4034   $249.40   $249.40   $249.40  
  Purchase #4 $72.35   6.527%   $77.0723   $77.07   $77.05   $77.10  
  Purchase #5 $24.49   10.434%   $27.0453   $27.05   $27.05   $27.00  
  Purchase #6 $62.25   3.556%   $64.4636   $64.46   $64.45   $64.50  
  Purchase #7 $201.73   4.804%   $211.4211   $211.42   $211.40   $211.40  
  7 purchase totals = $820.82       $876.3594   $876.35   $876.30   $876.30