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 $98.55   3.817%   $102.3117   $102.31   $102.30   $102.30  
  Purchase #2 $13.29   11.211%   $14.7799   $14.78   $14.80   $14.80  
  Purchase #3 $71.56   6.766%   $76.4017   $76.40   $76.40   $76.40  
  Purchase #4 $154.72   6.465%   $164.7226   $164.72   $164.70   $164.70  
  Purchase #5 $212.63   12.604%   $239.4299   $239.43   $239.45   $239.40  
  Purchase #6 $113.35   5.633%   $119.735   $119.74   $119.75   $119.70  
  Purchase #7 $32.61   4.528%   $34.0866   $34.09   $34.10   $34.10  
  7 purchase totals = $696.71       $751.4674   $751.47   $751.50   $751.40