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 $222.37   8.387%   $241.0202   $241.02   $241.00   $241.00  
  Purchase #2 $75.58   3.828%   $78.4732   $78.47   $78.45   $78.50  
  Purchase #3 $85.91   9.431%   $94.0122   $94.01   $94.00   $94.00  
  Purchase #4 $168.73   8.352%   $182.8223   $182.82   $182.80   $182.80  
  Purchase #5 $135.63   9.568%   $148.6071   $148.61   $148.60   $148.60  
  Purchase #6 $90.48   12.636%   $101.9131   $101.91   $101.90   $101.90  
  Purchase #7 $138.41   7.716%   $149.0897   $149.09   $149.10   $149.10  
  7 purchase totals = $917.11       $995.9378   $995.93   $995.85   $995.90