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 $126.63   12.152%   $142.0181   $142.02   $142.00   $142.00  
  Purchase #2 $130.63   4.123%   $136.0159   $136.02   $136.00   $136.00  
  Purchase #3 $186.82   10.729%   $206.8639   $206.86   $206.85   $206.90  
  Purchase #4 $83.62   8.606%   $90.8163   $90.82   $90.80   $90.80  
  Purchase #5 $34.66   5.570%   $36.5906   $36.59   $36.60   $36.60  
  Purchase #6 $188.29   9.574%   $206.3169   $206.32   $206.30   $206.30  
  Purchase #7 $45.30   3.181%   $46.741   $46.74   $46.75   $46.70  
  7 purchase totals = $795.95       $865.3627   $865.37   $865.30   $865.30