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 $67.82   12.145%   $76.0567   $76.06   $76.05   $76.10  
  Purchase #2 $119.31   4.490%   $124.667   $124.67   $124.65   $124.70  
  Purchase #3 $189.91   3.180%   $195.9491   $195.95   $195.95   $195.90  
  Purchase #4 $73.25   8.187%   $79.247   $79.25   $79.25   $79.20  
  Purchase #5 $20.53   4.231%   $21.3986   $21.40   $21.40   $21.40  
  Purchase #6 $64.64   5.260%   $68.0401   $68.04   $68.05   $68.00  
  Purchase #7 $169.49   8.127%   $183.2645   $183.26   $183.25   $183.30  
  7 purchase totals = $704.95       $748.6230   $748.63   $748.60   $748.60