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 $13.41   9.313%   $14.6589   $14.66   $14.65   $14.70  
  Purchase #2 $191.32   8.118%   $206.8514   $206.85   $206.85   $206.90  
  Purchase #3 $154.31   7.543%   $165.9496   $165.95   $165.95   $165.90  
  Purchase #4 $215.67   13.761%   $245.3483   $245.35   $245.35   $245.30  
  Purchase #5 $173.77   6.105%   $184.3787   $184.38   $184.40   $184.40  
  Purchase #6 $200.28   13.462%   $227.2417   $227.24   $227.25   $227.20  
  Purchase #7 $12.88   7.518%   $13.8483   $13.85   $13.85   $13.80  
  7 purchase totals = $961.64       $1,058.2769   $1,058.28   $1,058.30   $1,058.20