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 $98.33   3.185%   $101.4618   $101.46   $101.45   $101.50  
  Purchase #2 $23.92   3.317%   $24.7134   $24.71   $24.70   $24.70  
  Purchase #3 $156.53   10.419%   $172.8389   $172.84   $172.85   $172.80  
  Purchase #4 $177.91   3.359%   $183.886   $183.89   $183.90   $183.90  
  Purchase #5 $110.78   7.301%   $118.868   $118.87   $118.85   $118.90  
  Purchase #6 $19.66   10.201%   $21.6655   $21.67   $21.65   $21.70  
  Purchase #7 $133.87   4.694%   $140.1539   $140.15   $140.15   $140.20  
  7 purchase totals = $721.00       $763.5875   $763.59   $763.55   $763.70