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 $245.60   8.287%   $265.9529   $265.95   $265.95   $266.00  
  Purchase #2 $104.41   10.161%   $115.0191   $115.02   $115.00   $115.00  
  Purchase #3 $134.43   13.221%   $152.203   $152.20   $152.20   $152.20  
  Purchase #4 $38.86   5.509%   $41.0008   $41.00   $41.00   $41.00  
  Purchase #5 $20.69   10.310%   $22.8231   $22.82   $22.80   $22.80  
  Purchase #6 $95.83   9.737%   $105.161   $105.16   $105.15   $105.20  
  Purchase #7 $35.50   10.651%   $39.2811   $39.28   $39.30   $39.30  
  7 purchase totals = $675.32       $741.4410   $741.43   $741.40   $741.50