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 $209.95   12.127%   $235.4106   $235.41   $235.40   $235.40  
  Purchase #2 $190.58   6.259%   $202.5084   $202.51   $202.50   $202.50  
  Purchase #3 $169.54   5.412%   $178.7155   $178.72   $178.70   $178.70  
  Purchase #4 $243.80   7.207%   $261.3707   $261.37   $261.35   $261.40  
  Purchase #5 $242.31   10.140%   $266.8802   $266.88   $266.90   $266.90  
  Purchase #6 $195.62   11.598%   $218.308   $218.31   $218.30   $218.30  
  Purchase #7 $123.43   10.153%   $135.9618   $135.96   $135.95   $136.00  
  7 purchase totals = $1,375.23       $1,499.1552   $1,499.16   $1,499.10   $1,499.20