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 $75.93   9.327%   $83.012   $83.01   $83.00   $83.00  
  Purchase #2 $108.38   11.207%   $120.5261   $120.53   $120.55   $120.50  
  Purchase #3 $67.62   7.390%   $72.6171   $72.62   $72.60   $72.60  
  Purchase #4 $205.37   4.289%   $214.1783   $214.18   $214.20   $214.20  
  Purchase #5 $47.94   3.513%   $49.6241   $49.62   $49.60   $49.60  
  Purchase #6 $187.46   3.669%   $194.3379   $194.34   $194.35   $194.30  
  Purchase #7 $60.32   13.856%   $68.6779   $68.68   $68.70   $68.70  
  7 purchase totals = $753.02       $802.9734   $802.98   $803.00   $802.90