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 $114.33   3.176%   $117.9611   $117.96   $117.95   $118.00  
  Purchase #2 $109.99   5.687%   $116.2451   $116.25   $116.25   $116.20  
  Purchase #3 $120.32   8.557%   $130.6158   $130.62   $130.60   $130.60  
  Purchase #4 $199.49   5.537%   $210.5358   $210.54   $210.55   $210.50  
  Purchase #5 $104.94   10.745%   $116.2158   $116.22   $116.20   $116.20  
  Purchase #6 $153.72   8.850%   $167.3242   $167.32   $167.30   $167.30  
  Purchase #7 $66.62   5.720%   $70.4307   $70.43   $70.45   $70.40  
  7 purchase totals = $869.41       $929.3285   $929.34   $929.30   $929.20