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 $60.98   5.825%   $64.5321   $64.53   $64.55   $64.50  
  Purchase #2 $52.92   9.866%   $58.1411   $58.14   $58.15   $58.10  
  Purchase #3 $68.49   6.497%   $72.9398   $72.94   $72.95   $72.90  
  Purchase #4 $102.57   3.467%   $106.1261   $106.13   $106.15   $106.10  
  Purchase #5 $133.39   4.361%   $139.2071   $139.21   $139.20   $139.20  
  Purchase #6 $209.96   3.654%   $217.6319   $217.63   $217.65   $217.60  
  Purchase #7 $187.84   7.678%   $202.2624   $202.26   $202.25   $202.30  
  7 purchase totals = $816.15       $860.8405   $860.84   $860.90   $860.70