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 $104.75   13.696%   $119.0966   $119.10   $119.10   $119.10  
  Purchase #2 $141.76   7.443%   $152.3112   $152.31   $152.30   $152.30  
  Purchase #3 $194.87   8.358%   $211.1572   $211.16   $211.15   $211.20  
  Purchase #4 $160.56   13.423%   $182.112   $182.11   $182.10   $182.10  
  Purchase #5 $55.31   12.616%   $62.2879   $62.29   $62.30   $62.30  
  Purchase #6 $180.25   12.741%   $203.2157   $203.22   $203.20   $203.20  
  Purchase #7 $47.80   8.267%   $51.7516   $51.75   $51.75   $51.80  
  7 purchase totals = $885.30       $981.9322   $981.94   $981.90   $982.00