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 $81.87   13.285%   $92.7464   $92.75   $92.75   $92.70  
  Purchase #2 $109.97   3.451%   $113.7651   $113.77   $113.75   $113.80  
  Purchase #3 $120.43   13.265%   $136.405   $136.41   $136.40   $136.40  
  Purchase #4 $67.47   7.691%   $72.6591   $72.66   $72.65   $72.70  
  Purchase #5 $194.96   10.524%   $215.4776   $215.48   $215.50   $215.50  
  Purchase #6 $244.46   3.610%   $253.285   $253.29   $253.30   $253.30  
  Purchase #7 $154.63   13.798%   $175.9658   $175.97   $175.95   $176.00  
  7 purchase totals = $973.79       $1,060.3040   $1,060.33   $1,060.30   $1,060.40