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 $209.41   7.409%   $224.9252   $224.93   $224.95   $224.90  
  Purchase #2 $175.97   12.357%   $197.7146   $197.71   $197.70   $197.70  
  Purchase #3 $70.64   5.837%   $74.7633   $74.76   $74.75   $74.80  
  Purchase #4 $224.73   4.176%   $234.1147   $234.11   $234.10   $234.10  
  Purchase #5 $243.35   7.365%   $261.2727   $261.27   $261.25   $261.30  
  Purchase #6 $238.68   13.667%   $271.3004   $271.30   $271.30   $271.30  
  Purchase #7 $182.41   12.137%   $204.5491   $204.55   $204.55   $204.50  
  7 purchase totals = $1,345.19       $1,468.6400   $1,468.63   $1,468.60   $1,468.60