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 $234.41   13.122%   $265.1693   $265.17   $265.15   $265.20  
  Purchase #2 $27.69   8.867%   $30.1453   $30.15   $30.15   $30.10  
  Purchase #3 $122.62   13.467%   $139.1332   $139.13   $139.15   $139.10  
  Purchase #4 $175.42   4.750%   $183.7525   $183.75   $183.75   $183.80  
  Purchase #5 $69.63   4.814%   $72.982   $72.98   $73.00   $73.00  
  Purchase #6 $101.90   9.247%   $111.3227   $111.32   $111.30   $111.30  
  Purchase #7 $84.29   13.744%   $95.8748   $95.87   $95.85   $95.90  
  7 purchase totals = $815.96       $898.3798   $898.37   $898.35   $898.40