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 $196.46   13.164%   $222.322   $222.32   $222.30   $222.30  
  Purchase #2 $66.59   4.714%   $69.7291   $69.73   $69.75   $69.70  
  Purchase #3 $31.68   13.468%   $35.9467   $35.95   $35.95   $35.90  
  Purchase #4 $30.81   7.725%   $33.1901   $33.19   $33.20   $33.20  
  Purchase #5 $88.97   3.560%   $92.1373   $92.14   $92.15   $92.10  
  Purchase #6 $136.35   13.140%   $154.2664   $154.27   $154.25   $154.30  
  Purchase #7 $108.58   9.809%   $119.2306   $119.23   $119.25   $119.20  
  7 purchase totals = $659.44       $726.8222   $726.83   $726.85   $726.70