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 $94.58   3.596%   $97.9811   $97.98   $98.00   $98.00  
  Purchase #2 $239.71   7.263%   $257.1201   $257.12   $257.10   $257.10  
  Purchase #3 $139.49   9.853%   $153.2339   $153.23   $153.25   $153.20  
  Purchase #4 $221.90   3.606%   $229.9017   $229.90   $229.90   $229.90  
  Purchase #5 $119.34   8.855%   $129.9076   $129.91   $129.90   $129.90  
  Purchase #6 $71.90   7.406%   $77.2249   $77.22   $77.20   $77.20  
  Purchase #7 $37.26   9.389%   $40.7583   $40.76   $40.75   $40.80  
  7 purchase totals = $924.18       $986.1276   $986.12   $986.10   $986.10