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 $93.66   10.673%   $103.6563   $103.66   $103.65   $103.70  
  Purchase #2 $105.40   11.147%   $117.1489   $117.15   $117.15   $117.10  
  Purchase #3 $221.57   9.862%   $243.4212   $243.42   $243.40   $243.40  
  Purchase #4 $109.27   7.610%   $117.5854   $117.59   $117.60   $117.60  
  Purchase #5 $182.96   6.812%   $195.4232   $195.42   $195.40   $195.40  
  Purchase #6 $103.25   10.747%   $114.3463   $114.35   $114.35   $114.30  
  Purchase #7 $16.94   5.140%   $17.8107   $17.81   $17.80   $17.80  
  7 purchase totals = $833.05       $909.3920   $909.40   $909.35   $909.30