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 $141.30   10.413%   $156.0136   $156.01   $156.00   $156.00  
  Purchase #2 $222.69   10.434%   $245.9255   $245.93   $245.95   $245.90  
  Purchase #3 $185.63   5.462%   $195.7691   $195.77   $195.75   $195.80  
  Purchase #4 $69.47   13.435%   $78.8033   $78.80   $78.80   $78.80  
  Purchase #5 $30.68   9.526%   $33.6026   $33.60   $33.60   $33.60  
  Purchase #6 $6.59   8.593%   $7.1563   $7.16   $7.15   $7.20  
  Purchase #7 $206.47   13.658%   $234.6697   $234.67   $234.65   $234.70  
  7 purchase totals = $862.83       $951.9401   $951.94   $951.90   $952.00