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 $74.74   3.868%   $77.6309   $77.63   $77.65   $77.60  
  Purchase #2 $213.69   10.520%   $236.1702   $236.17   $236.15   $236.20  
  Purchase #3 $153.78   7.564%   $165.4119   $165.41   $165.40   $165.40  
  Purchase #4 $115.46   4.451%   $120.5991   $120.60   $120.60   $120.60  
  Purchase #5 $18.73   9.858%   $20.5764   $20.58   $20.60   $20.60  
  Purchase #6 $55.26   13.512%   $62.7267   $62.73   $62.75   $62.70  
  Purchase #7 $34.90   11.317%   $38.8496   $38.85   $38.85   $38.80  
  7 purchase totals = $666.56       $721.9648   $721.97   $722.00   $721.90