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 $246.95   5.263%   $259.947   $259.95   $259.95   $259.90  
  Purchase #2 $38.66   5.430%   $40.7592   $40.76   $40.75   $40.80  
  Purchase #3 $103.32   10.501%   $114.1696   $114.17   $114.15   $114.20  
  Purchase #4 $37.74   6.825%   $40.3158   $40.32   $40.30   $40.30  
  Purchase #5 $167.90   9.793%   $184.3424   $184.34   $184.35   $184.30  
  Purchase #6 $191.37   11.701%   $213.7622   $213.76   $213.75   $213.80  
  Purchase #7 $91.74   6.712%   $97.8976   $97.90   $97.90   $97.90  
  7 purchase totals = $877.68       $951.1938   $951.20   $951.15   $951.20