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   10.243%   $74.8991   $74.90   $74.90   $74.90  
  Purchase #2 $56.36   11.608%   $62.9023   $62.90   $62.90   $62.90  
  Purchase #3 $108.66   8.728%   $118.1438   $118.14   $118.15   $118.10  
  Purchase #4 $233.90   4.584%   $244.622   $244.62   $244.60   $244.60  
  Purchase #5 $108.73   9.632%   $119.2029   $119.20   $119.20   $119.20  
  Purchase #6 $235.41   13.834%   $267.9766   $267.98   $268.00   $268.00  
  Purchase #7 $10.26   3.737%   $10.6434   $10.64   $10.65   $10.60  
  7 purchase totals = $821.26       $898.3901   $898.38   $898.40   $898.30