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 $54.56   10.266%   $60.1611   $60.16   $60.15   $60.20  
  Purchase #2 $76.90   9.538%   $84.2347   $84.23   $84.25   $84.20  
  Purchase #3 $232.27   10.680%   $257.0764   $257.08   $257.10   $257.10  
  Purchase #4 $240.49   11.141%   $267.283   $267.28   $267.30   $267.30  
  Purchase #5 $187.49   13.766%   $213.2999   $213.30   $213.30   $213.30  
  Purchase #6 $186.67   10.210%   $205.729   $205.73   $205.75   $205.70  
  Purchase #7 $157.58   5.131%   $165.6654   $165.67   $165.65   $165.70  
  7 purchase totals = $1,135.96       $1,253.4495   $1,253.45   $1,253.50   $1,253.50