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 $182.66   13.686%   $207.6588   $207.66   $207.65   $207.70  
  Purchase #2 $31.38   12.449%   $35.2865   $35.29   $35.30   $35.30  
  Purchase #3 $128.86   3.425%   $133.2735   $133.27   $133.25   $133.30  
  Purchase #4 $43.37   9.803%   $47.6216   $47.62   $47.60   $47.60  
  Purchase #5 $167.45   13.684%   $190.3639   $190.36   $190.35   $190.40  
  Purchase #6 $203.27   11.860%   $227.3778   $227.38   $227.40   $227.40  
  Purchase #7 $109.25   4.770%   $114.4612   $114.46   $114.45   $114.50  
  7 purchase totals = $866.24       $956.0433   $956.04   $956.00   $956.20