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 $57.70   11.312%   $64.227   $64.23   $64.25   $64.20  
  Purchase #2 $121.87   8.309%   $131.9962   $132.00   $132.00   $132.00  
  Purchase #3 $60.67   8.549%   $65.8567   $65.86   $65.85   $65.90  
  Purchase #4 $180.81   4.274%   $188.5378   $188.54   $188.55   $188.50  
  Purchase #5 $221.96   12.714%   $250.18   $250.18   $250.20   $250.20  
  Purchase #6 $146.32   9.240%   $159.84   $159.84   $159.85   $159.80  
  Purchase #7 $19.39   11.611%   $21.6414   $21.64   $21.65   $21.60  
  7 purchase totals = $808.72       $882.2791   $882.29   $882.35   $882.20