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 $249.92   4.848%   $262.0361   $262.04   $262.05   $262.00  
  Purchase #2 $11.98   11.348%   $13.3395   $13.34   $13.35   $13.30  
  Purchase #3 $111.86   12.288%   $125.6054   $125.61   $125.60   $125.60  
  Purchase #4 $245.86   11.863%   $275.0264   $275.03   $275.05   $275.00  
  Purchase #5 $33.59   4.764%   $35.1902   $35.19   $35.20   $35.20  
  Purchase #6 $32.65   9.381%   $35.7129   $35.71   $35.70   $35.70  
  Purchase #7 $68.68   8.304%   $74.3832   $74.38   $74.40   $74.40  
  7 purchase totals = $754.54       $821.2937   $821.30   $821.35   $821.20