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 $73.72   4.347%   $76.9246   $76.92   $76.90   $76.90  
  Purchase #2 $232.38   6.147%   $246.6644   $246.66   $246.65   $246.70  
  Purchase #3 $76.61   10.841%   $84.9153   $84.92   $84.90   $84.90  
  Purchase #4 $107.47   4.633%   $112.4491   $112.45   $112.45   $112.40  
  Purchase #5 $131.97   8.734%   $143.4963   $143.50   $143.50   $143.50  
  Purchase #6 $225.87   13.614%   $256.6199   $256.62   $256.60   $256.60  
  Purchase #7 $139.76   8.186%   $151.2008   $151.20   $151.20   $151.20  
  7 purchase totals = $987.78       $1,072.2704   $1,072.27   $1,072.20   $1,072.20