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 $59.83   5.838%   $63.3229   $63.32   $63.30   $63.30  
  Purchase #2 $197.92   3.430%   $204.7087   $204.71   $204.70   $204.70  
  Purchase #3 $231.50   13.573%   $262.9215   $262.92   $262.90   $262.90  
  Purchase #4 $159.86   8.699%   $173.7662   $173.77   $173.75   $173.80  
  Purchase #5 $105.58   12.687%   $118.9749   $118.97   $118.95   $119.00  
  Purchase #6 $210.96   11.854%   $235.9672   $235.97   $235.95   $236.00  
  Purchase #7 $242.99   7.451%   $261.0952   $261.10   $261.10   $261.10  
  7 purchase totals = $1,208.64       $1,320.7566   $1,320.76   $1,320.65   $1,320.80