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 $9.46   4.350%   $9.8715   $9.87   $9.85   $9.90  
  Purchase #2 $188.38   3.765%   $195.4725   $195.47   $195.45   $195.50  
  Purchase #3 $28.68   3.234%   $29.6075   $29.61   $29.60   $29.60  
  Purchase #4 $150.55   12.238%   $168.9743   $168.97   $168.95   $169.00  
  Purchase #5 $141.61   9.160%   $154.5815   $154.58   $154.60   $154.60  
  Purchase #6 $29.38   3.302%   $30.3501   $30.35   $30.35   $30.40  
  Purchase #7 $17.71   5.622%   $18.7057   $18.71   $18.70   $18.70  
  7 purchase totals = $565.77       $607.5631   $607.56   $607.50   $607.70