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 $61.51   9.302%   $67.2317   $67.23   $67.25   $67.20  
  Purchase #2 $69.71   4.825%   $73.0735   $73.07   $73.05   $73.10  
  Purchase #3 $241.35   10.438%   $266.5421   $266.54   $266.55   $266.50  
  Purchase #4 $32.55   5.333%   $34.2859   $34.29   $34.30   $34.30  
  Purchase #5 $27.54   13.558%   $31.2739   $31.27   $31.25   $31.30  
  Purchase #6 $152.81   13.548%   $173.5127   $173.51   $173.50   $173.50  
  Purchase #7 $166.26   9.512%   $182.0747   $182.07   $182.05   $182.10  
  7 purchase totals = $751.73       $827.9945   $827.98   $827.95   $828.00