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 $93.73   12.602%   $105.5419   $105.54   $105.55   $105.50  
  Purchase #2 $99.54   10.682%   $110.1729   $110.17   $110.15   $110.20  
  Purchase #3 $149.44   6.861%   $159.6931   $159.69   $159.70   $159.70  
  Purchase #4 $66.64   10.497%   $73.6352   $73.64   $73.65   $73.60  
  Purchase #5 $214.43   9.124%   $233.9946   $233.99   $234.00   $234.00  
  Purchase #6 $53.41   9.106%   $58.2735   $58.27   $58.25   $58.30  
  Purchase #7 $167.28   9.192%   $182.6564   $182.66   $182.65   $182.70  
  7 purchase totals = $844.47       $923.9676   $923.96   $923.95   $924.00