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 $116.42   13.271%   $131.8701   $131.87   $131.85   $131.90  
  Purchase #2 $103.43   8.142%   $111.8513   $111.85   $111.85   $111.90  
  Purchase #3 $46.93   3.634%   $48.6354   $48.64   $48.65   $48.60  
  Purchase #4 $216.99   5.614%   $229.1718   $229.17   $229.15   $229.20  
  Purchase #5 $193.90   8.303%   $209.9995   $210.00   $210.00   $210.00  
  Purchase #6 $85.76   3.467%   $88.7333   $88.73   $88.75   $88.70  
  Purchase #7 $106.28   12.629%   $119.7021   $119.70   $119.70   $119.70  
  7 purchase totals = $869.71       $939.9635   $939.96   $939.95   $940.00