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 $47.32   13.220%   $53.5757   $53.58   $53.60   $53.60  
  Purchase #2 $109.43   12.154%   $122.7301   $122.73   $122.75   $122.70  
  Purchase #3 $33.55   8.543%   $36.4162   $36.42   $36.40   $36.40  
  Purchase #4 $246.48   8.117%   $266.4868   $266.49   $266.50   $266.50  
  Purchase #5 $104.39   13.204%   $118.1737   $118.17   $118.15   $118.20  
  Purchase #6 $42.44   10.777%   $47.0138   $47.01   $47.00   $47.00  
  Purchase #7 $46.36   10.680%   $51.3112   $51.31   $51.30   $51.30  
  7 purchase totals = $629.97       $695.7075   $695.71   $695.70   $695.70