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 $89.41   5.424%   $94.2596   $94.26   $94.25   $94.30  
  Purchase #2 $116.44   3.810%   $120.8764   $120.88   $120.90   $120.90  
  Purchase #3 $151.70   11.671%   $169.4049   $169.40   $169.40   $169.40  
  Purchase #4 $146.33   5.408%   $154.2435   $154.24   $154.25   $154.20  
  Purchase #5 $207.40   4.324%   $216.368   $216.37   $216.35   $216.40  
  Purchase #6 $8.48   9.398%   $9.277   $9.28   $9.30   $9.30  
  Purchase #7 $164.88   11.857%   $184.4298   $184.43   $184.45   $184.40  
  7 purchase totals = $884.64       $948.8592   $948.86   $948.90   $948.90