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 $206.87   12.725%   $233.1942   $233.19   $233.20   $233.20  
  Purchase #2 $167.71   10.566%   $185.4302   $185.43   $185.45   $185.40  
  Purchase #3 $245.30   12.499%   $275.96   $275.96   $275.95   $276.00  
  Purchase #4 $173.97   7.344%   $186.7464   $186.75   $186.75   $186.70  
  Purchase #5 $236.90   7.163%   $253.8691   $253.87   $253.85   $253.90  
  Purchase #6 $56.54   5.353%   $59.5666   $59.57   $59.55   $59.60  
  Purchase #7 $27.63   10.872%   $30.6339   $30.63   $30.65   $30.60  
  7 purchase totals = $1,114.92       $1,225.4004   $1,225.40   $1,225.40   $1,225.40