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 $67.94   12.548%   $76.4651   $76.47   $76.45   $76.50  
  Purchase #2 $104.87   8.618%   $113.9077   $113.91   $113.90   $113.90  
  Purchase #3 $143.33   6.355%   $152.4386   $152.44   $152.45   $152.40  
  Purchase #4 $190.64   11.441%   $212.4511   $212.45   $212.45   $212.50  
  Purchase #5 $134.29   6.529%   $143.0578   $143.06   $143.05   $143.10  
  Purchase #6 $157.26   11.356%   $175.1184   $175.12   $175.10   $175.10  
  Purchase #7 $47.89   12.831%   $54.0348   $54.03   $54.05   $54.00  
  7 purchase totals = $846.22       $927.4735   $927.48   $927.45   $927.50