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 $161.61   13.247%   $183.0185   $183.02   $183.00   $183.00  
  Purchase #2 $25.73   13.563%   $29.2198   $29.22   $29.20   $29.20  
  Purchase #3 $20.64   10.244%   $22.7544   $22.75   $22.75   $22.80  
  Purchase #4 $93.54   5.559%   $98.7399   $98.74   $98.75   $98.70  
  Purchase #5 $95.27   3.609%   $98.7083   $98.71   $98.70   $98.70  
  Purchase #6 $165.86   4.306%   $173.0019   $173.00   $173.00   $173.00  
  Purchase #7 $27.65   9.195%   $30.1924   $30.19   $30.20   $30.20  
  7 purchase totals = $590.30       $635.6352   $635.63   $635.60   $635.60