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 $231.98   9.204%   $253.3314   $253.33   $253.35   $253.30  
  Purchase #2 $54.99   8.333%   $59.5723   $59.57   $59.55   $59.60  
  Purchase #3 $52.97   13.716%   $60.2354   $60.24   $60.25   $60.20  
  Purchase #4 $84.32   5.773%   $89.1878   $89.19   $89.20   $89.20  
  Purchase #5 $32.59   5.157%   $34.2707   $34.27   $34.25   $34.30  
  Purchase #6 $9.29   4.826%   $9.7383   $9.74   $9.75   $9.70  
  Purchase #7 $225.89   13.745%   $256.9386   $256.94   $256.95   $256.90  
  7 purchase totals = $692.03       $763.2745   $763.28   $763.30   $763.20