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 $104.83   10.769%   $116.1191   $116.12   $116.10   $116.10  
  Purchase #2 $173.55   11.558%   $193.6089   $193.61   $193.60   $193.60  
  Purchase #3 $189.86   10.335%   $209.482   $209.48   $209.50   $209.50  
  Purchase #4 $179.39   7.752%   $193.2963   $193.30   $193.30   $193.30  
  Purchase #5 $107.57   11.455%   $119.8921   $119.89   $119.90   $119.90  
  Purchase #6 $109.47   4.628%   $114.5363   $114.54   $114.55   $114.50  
  Purchase #7 $35.92   6.492%   $38.2519   $38.25   $38.25   $38.30  
  7 purchase totals = $900.59       $985.1866   $985.19   $985.20   $985.20