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 $216.48   11.862%   $242.1589   $242.16   $242.15   $242.20  
  Purchase #2 $119.34   3.153%   $123.1028   $123.10   $123.10   $123.10  
  Purchase #3 $235.90   4.140%   $245.6663   $245.67   $245.65   $245.70  
  Purchase #4 $69.41   10.406%   $76.6328   $76.63   $76.65   $76.60  
  Purchase #5 $55.64   5.167%   $58.5149   $58.51   $58.50   $58.50  
  Purchase #6 $95.41   7.808%   $102.8596   $102.86   $102.85   $102.90  
  Purchase #7 $15.37   10.749%   $17.0221   $17.02   $17.00   $17.00  
  7 purchase totals = $807.55       $865.9574   $865.95   $865.90   $866.00