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 $217.49   13.837%   $247.5841   $247.58   $247.60   $247.60  
  Purchase #2 $53.26   10.212%   $58.6989   $58.70   $58.70   $58.70  
  Purchase #3 $119.38   11.746%   $133.4024   $133.40   $133.40   $133.40  
  Purchase #4 $127.60   9.420%   $139.6199   $139.62   $139.60   $139.60  
  Purchase #5 $231.40   13.394%   $262.3937   $262.39   $262.40   $262.40  
  Purchase #6 $166.47   4.245%   $173.5367   $173.54   $173.55   $173.50  
  Purchase #7 $205.44   11.781%   $229.6429   $229.64   $229.65   $229.60  
  7 purchase totals = $1,121.04       $1,244.8786   $1,244.87   $1,244.90   $1,244.80