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 $195.30   11.539%   $217.8357   $217.84   $217.85   $217.80  
  Purchase #2 $119.66   4.406%   $124.9322   $124.93   $124.95   $124.90  
  Purchase #3 $6.55   13.405%   $7.428   $7.43   $7.45   $7.40  
  Purchase #4 $234.33   9.663%   $256.9733   $256.97   $256.95   $257.00  
  Purchase #5 $164.45   11.503%   $183.3667   $183.37   $183.35   $183.40  
  Purchase #6 $112.97   5.590%   $119.285   $119.29   $119.30   $119.30  
  Purchase #7 $118.77   5.822%   $125.6848   $125.68   $125.70   $125.70  
  7 purchase totals = $952.03       $1,035.5057   $1,035.51   $1,035.55   $1,035.50