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 $129.65   12.758%   $146.1907   $146.19   $146.20   $146.20  
  Purchase #2 $244.28   6.831%   $260.9668   $260.97   $260.95   $261.00  
  Purchase #3 $66.76   7.516%   $71.7777   $71.78   $71.80   $71.80  
  Purchase #4 $102.51   12.212%   $115.0285   $115.03   $115.05   $115.00  
  Purchase #5 $25.36   11.650%   $28.3144   $28.31   $28.30   $28.30  
  Purchase #6 $33.77   4.212%   $35.1924   $35.19   $35.20   $35.20  
  Purchase #7 $201.64   9.208%   $220.207   $220.21   $220.20   $220.20  
  7 purchase totals = $803.97       $877.6775   $877.68   $877.70   $877.70