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 $137.41   12.496%   $154.5808   $154.58   $154.60   $154.60  
  Purchase #2 $216.89   13.303%   $245.7429   $245.74   $245.75   $245.70  
  Purchase #3 $250.79   10.135%   $276.2076   $276.21   $276.20   $276.20  
  Purchase #4 $173.25   6.138%   $183.8841   $183.88   $183.90   $183.90  
  Purchase #5 $182.47   4.598%   $190.86   $190.86   $190.85   $190.90  
  Purchase #6 $225.50   10.311%   $248.7513   $248.75   $248.75   $248.80  
  Purchase #7 $126.87   7.432%   $136.299   $136.30   $136.30   $136.30  
  7 purchase totals = $1,313.18       $1,436.3257   $1,436.32   $1,436.35   $1,436.40