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 $241.46   13.674%   $274.4772   $274.48   $274.50   $274.50  
  Purchase #2 $90.56   8.849%   $98.5737   $98.57   $98.55   $98.60  
  Purchase #3 $215.93   6.400%   $229.7495   $229.75   $229.75   $229.70  
  Purchase #4 $33.41   6.460%   $35.5683   $35.57   $35.55   $35.60  
  Purchase #5 $151.61   5.106%   $159.3512   $159.35   $159.35   $159.40  
  Purchase #6 $116.33   13.689%   $132.2544   $132.25   $132.25   $132.30  
  Purchase #7 $62.78   8.619%   $68.191   $68.19   $68.20   $68.20  
  7 purchase totals = $912.08       $998.1653   $998.16   $998.15   $998.30