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 $220.40   9.349%   $241.0052   $241.01   $241.00   $241.00  
  Purchase #2 $162.47   6.620%   $173.2255   $173.23   $173.25   $173.20  
  Purchase #3 $56.34   7.823%   $60.7475   $60.75   $60.75   $60.70  
  Purchase #4 $133.88   9.132%   $146.1059   $146.11   $146.10   $146.10  
  Purchase #5 $149.32   6.179%   $158.5465   $158.55   $158.55   $158.50  
  Purchase #6 $128.32   6.507%   $136.6698   $136.67   $136.65   $136.70  
  Purchase #7 $32.54   9.179%   $35.5268   $35.53   $35.55   $35.50  
  7 purchase totals = $883.27       $951.8272   $951.85   $951.85   $951.70