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 $125.73   5.403%   $132.5232   $132.52   $132.50   $132.50  
  Purchase #2 $63.79   3.341%   $65.9212   $65.92   $65.90   $65.90  
  Purchase #3 $134.53   6.732%   $143.5866   $143.59   $143.60   $143.60  
  Purchase #4 $91.50   11.251%   $101.7947   $101.79   $101.80   $101.80  
  Purchase #5 $60.26   8.248%   $65.2302   $65.23   $65.25   $65.20  
  Purchase #6 $65.74   11.521%   $73.3139   $73.31   $73.30   $73.30  
  Purchase #7 $229.68   8.490%   $249.1798   $249.18   $249.20   $249.20  
  7 purchase totals = $771.23       $831.5496   $831.54   $831.55   $831.50