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 $86.32   10.622%   $95.4889   $95.49   $95.50   $95.50  
  Purchase #2 $215.29   4.117%   $224.1535   $224.15   $224.15   $224.20  
  Purchase #3 $69.81   11.206%   $77.6329   $77.63   $77.65   $77.60  
  Purchase #4 $156.79   6.442%   $166.8904   $166.89   $166.90   $166.90  
  Purchase #5 $30.92   12.259%   $34.7105   $34.71   $34.70   $34.70  
  Purchase #6 $81.53   3.273%   $84.1985   $84.20   $84.20   $84.20  
  Purchase #7 $131.40   8.633%   $142.7438   $142.74   $142.75   $142.70  
  7 purchase totals = $772.06       $825.8185   $825.81   $825.85   $825.80