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 $84.44   13.302%   $95.6722   $95.67   $95.65   $95.70  
  Purchase #2 $57.68   3.477%   $59.6855   $59.69   $59.70   $59.70  
  Purchase #3 $248.63   6.108%   $263.8163   $263.82   $263.80   $263.80  
  Purchase #4 $79.40   9.487%   $86.9327   $86.93   $86.95   $86.90  
  Purchase #5 $11.96   8.304%   $12.9532   $12.95   $12.95   $13.00  
  Purchase #6 $114.90   8.619%   $124.8032   $124.80   $124.80   $124.80  
  Purchase #7 $148.50   3.205%   $153.2594   $153.26   $153.25   $153.30  
  7 purchase totals = $745.51       $797.1225   $797.12   $797.10   $797.20