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 $172.70   13.343%   $195.7434   $195.74   $195.75   $195.70  
  Purchase #2 $103.26   6.245%   $109.7086   $109.71   $109.70   $109.70  
  Purchase #3 $41.73   13.588%   $47.4003   $47.40   $47.40   $47.40  
  Purchase #4 $49.42   13.667%   $56.1742   $56.17   $56.15   $56.20  
  Purchase #5 $88.45   5.570%   $93.3767   $93.38   $93.40   $93.40  
  Purchase #6 $42.43   13.661%   $48.2264   $48.23   $48.25   $48.20  
  Purchase #7 $41.33   3.134%   $42.6253   $42.63   $42.65   $42.60  
  7 purchase totals = $539.32       $593.2549   $593.26   $593.30   $593.20