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 $23.61   10.134%   $26.0026   $26.00   $26.00   $26.00  
  Purchase #2 $82.62   12.286%   $92.7707   $92.77   $92.75   $92.80  
  Purchase #3 $95.59   9.152%   $104.3384   $104.34   $104.35   $104.30  
  Purchase #4 $17.36   6.477%   $18.4844   $18.48   $18.50   $18.50  
  Purchase #5 $190.31   13.577%   $216.1484   $216.15   $216.15   $216.10  
  Purchase #6 $209.85   5.226%   $220.8168   $220.82   $220.80   $220.80  
  Purchase #7 $13.61   11.754%   $15.2097   $15.21   $15.20   $15.20  
  7 purchase totals = $632.95       $693.7710   $693.77   $693.75   $693.70