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 $84.64   11.454%   $94.3347   $94.33   $94.35   $94.30  
  Purchase #2 $233.39   3.358%   $241.2272   $241.23   $241.25   $241.20  
  Purchase #3 $130.62   13.868%   $148.7344   $148.73   $148.75   $148.70  
  Purchase #4 $88.65   11.108%   $98.4972   $98.50   $98.50   $98.50  
  Purchase #5 $117.36   8.457%   $127.2851   $127.29   $127.30   $127.30  
  Purchase #6 $229.36   5.735%   $242.5138   $242.51   $242.50   $242.50  
  Purchase #7 $50.38   7.518%   $54.1676   $54.17   $54.15   $54.20  
  7 purchase totals = $934.40       $1,006.7600   $1,006.76   $1,006.80   $1,006.70