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 $106.27   12.231%   $119.2679   $119.27   $119.25   $119.30  
  Purchase #2 $108.82   11.142%   $120.9447   $120.94   $120.95   $120.90  
  Purchase #3 $177.95   12.105%   $199.4908   $199.49   $199.50   $199.50  
  Purchase #4 $173.51   8.154%   $187.658   $187.66   $187.65   $187.70  
  Purchase #5 $125.60   11.135%   $139.5856   $139.59   $139.60   $139.60  
  Purchase #6 $93.27   8.664%   $101.3509   $101.35   $101.35   $101.40  
  Purchase #7 $37.42   13.161%   $42.3448   $42.34   $42.35   $42.30  
  7 purchase totals = $822.84       $910.6427   $910.64   $910.65   $910.70