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 $32.25   12.677%   $36.3383   $36.34   $36.35   $36.30  
  Purchase #2 $232.73   7.683%   $250.6106   $250.61   $250.60   $250.60  
  Purchase #3 $90.31   3.756%   $93.702   $93.70   $93.70   $93.70  
  Purchase #4 $129.56   13.229%   $146.6995   $146.70   $146.70   $146.70  
  Purchase #5 $75.37   9.143%   $82.2611   $82.26   $82.25   $82.30  
  Purchase #6 $8.82   5.514%   $9.3063   $9.31   $9.30   $9.30  
  Purchase #7 $71.81   3.590%   $74.388   $74.39   $74.40   $74.40  
  7 purchase totals = $640.85       $693.3058   $693.31   $693.30   $693.30