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 $23.74   8.867%   $25.845   $25.85   $25.85   $25.80  
  Purchase #2 $182.98   7.113%   $195.9954   $196.00   $196.00   $196.00  
  Purchase #3 $64.86   7.505%   $69.7277   $69.73   $69.75   $69.70  
  Purchase #4 $88.50   4.244%   $92.2559   $92.26   $92.25   $92.30  
  Purchase #5 $19.92   10.394%   $21.9905   $21.99   $22.00   $22.00  
  Purchase #6 $141.88   6.428%   $151   $151.00   $151.00   $151.00  
  Purchase #7 $53.43   5.432%   $56.3323   $56.33   $56.35   $56.30  
  7 purchase totals = $575.31       $613.1468   $613.16   $613.20   $613.10