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 $22.82   13.735%   $25.9543   $25.95   $25.95   $26.00  
  Purchase #2 $118.28   11.659%   $132.0703   $132.07   $132.05   $132.10  
  Purchase #3 $126.70   8.190%   $137.0767   $137.08   $137.10   $137.10  
  Purchase #4 $93.60   5.488%   $98.7368   $98.74   $98.75   $98.70  
  Purchase #5 $64.96   3.635%   $67.3213   $67.32   $67.30   $67.30  
  Purchase #6 $66.72   10.589%   $73.785   $73.79   $73.80   $73.80  
  Purchase #7 $49.63   9.409%   $54.2997   $54.30   $54.30   $54.30  
  7 purchase totals = $542.71       $589.2441   $589.25   $589.25   $589.30