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 $54.81   10.744%   $60.6988   $60.70   $60.70   $60.70  
  Purchase #2 $161.74   4.531%   $169.0684   $169.07   $169.05   $169.10  
  Purchase #3 $6.76   9.610%   $7.4096   $7.41   $7.40   $7.40  
  Purchase #4 $235.63   7.639%   $253.6298   $253.63   $253.65   $253.60  
  Purchase #5 $44.95   4.506%   $46.9754   $46.98   $47.00   $47.00  
  Purchase #6 $66.96   6.862%   $71.5548   $71.55   $71.55   $71.60  
  Purchase #7 $231.39   3.684%   $239.9144   $239.91   $239.90   $239.90  
  7 purchase totals = $802.24       $849.2512   $849.25   $849.25   $849.30