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 $44.43   12.622%   $50.038   $50.04   $50.05   $50.00  
  Purchase #2 $203.77   10.162%   $224.4771   $224.48   $224.50   $224.50  
  Purchase #3 $93.40   4.317%   $97.4321   $97.43   $97.45   $97.40  
  Purchase #4 $81.88   6.117%   $86.8886   $86.89   $86.90   $86.90  
  Purchase #5 $128.76   7.187%   $138.014   $138.01   $138.00   $138.00  
  Purchase #6 $202.34   5.497%   $213.4626   $213.46   $213.45   $213.50  
  Purchase #7 $125.44   6.418%   $133.4907   $133.49   $133.50   $133.50  
  7 purchase totals = $880.02       $943.8031   $943.80   $943.85   $943.80