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 $62.47   7.242%   $66.9941   $66.99   $67.00   $67.00  
  Purchase #2 $64.71   7.770%   $69.738   $69.74   $69.75   $69.70  
  Purchase #3 $188.73   11.615%   $210.651   $210.65   $210.65   $210.70  
  Purchase #4 $73.87   8.178%   $79.9111   $79.91   $79.90   $79.90  
  Purchase #5 $226.30   4.519%   $236.5265   $236.53   $236.55   $236.50  
  Purchase #6 $57.35   10.330%   $63.2743   $63.27   $63.25   $63.30  
  Purchase #7 $248.86   11.168%   $276.6527   $276.65   $276.65   $276.70  
  7 purchase totals = $922.29       $1,003.7477   $1,003.74   $1,003.75   $1,003.80