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 $67.72   6.729%   $72.2769   $72.28   $72.30   $72.30  
  Purchase #2 $229.53   5.275%   $241.6377   $241.64   $241.65   $241.60  
  Purchase #3 $219.42   4.468%   $229.2237   $229.22   $229.20   $229.20  
  Purchase #4 $98.77   11.265%   $109.8964   $109.90   $109.90   $109.90  
  Purchase #5 $132.35   5.234%   $139.2772   $139.28   $139.30   $139.30  
  Purchase #6 $159.75   3.678%   $165.6256   $165.63   $165.65   $165.60  
  Purchase #7 $206.38   12.541%   $232.2621   $232.26   $232.25   $232.30  
  7 purchase totals = $1,113.92       $1,190.1996   $1,190.21   $1,190.25   $1,190.20