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 $61.68   7.660%   $66.4047   $66.40   $66.40   $66.40  
  Purchase #2 $108.94   11.266%   $121.2132   $121.21   $121.20   $121.20  
  Purchase #3 $241.53   8.633%   $262.3813   $262.38   $262.40   $262.40  
  Purchase #4 $146.34   13.612%   $166.2598   $166.26   $166.25   $166.30  
  Purchase #5 $128.33   4.807%   $134.4988   $134.50   $134.50   $134.50  
  Purchase #6 $212.27   13.858%   $241.6864   $241.69   $241.70   $241.70  
  Purchase #7 $118.35   13.471%   $134.2929   $134.29   $134.30   $134.30  
  7 purchase totals = $1,017.44       $1,126.7371   $1,126.73   $1,126.75   $1,126.80