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 $246.84   5.852%   $261.2851   $261.29   $261.30   $261.30  
  Purchase #2 $98.30   3.279%   $101.5233   $101.52   $101.50   $101.50  
  Purchase #3 $101.40   3.638%   $105.0889   $105.09   $105.10   $105.10  
  Purchase #4 $185.85   5.191%   $195.4975   $195.50   $195.50   $195.50  
  Purchase #5 $131.98   10.781%   $146.2088   $146.21   $146.20   $146.20  
  Purchase #6 $248.38   12.396%   $279.1692   $279.17   $279.15   $279.20  
  Purchase #7 $217.71   3.443%   $225.2058   $225.21   $225.20   $225.20  
  7 purchase totals = $1,230.46       $1,313.9786   $1,313.99   $1,313.95   $1,314.00