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 $215.51   13.418%   $244.4271   $244.43   $244.45   $244.40  
  Purchase #2 $114.60   10.667%   $126.8244   $126.82   $126.80   $126.80  
  Purchase #3 $194.72   4.546%   $203.572   $203.57   $203.55   $203.60  
  Purchase #4 $248.47   3.583%   $257.3727   $257.37   $257.35   $257.40  
  Purchase #5 $181.25   8.865%   $197.3178   $197.32   $197.30   $197.30  
  Purchase #6 $173.68   8.713%   $188.8127   $188.81   $188.80   $188.80  
  Purchase #7 $21.37   3.833%   $22.1891   $22.19   $22.20   $22.20  
  7 purchase totals = $1,149.60       $1,240.5158   $1,240.51   $1,240.45   $1,240.50