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 $80.83   6.586%   $86.1535   $86.15   $86.15   $86.20  
  Purchase #2 $162.33   12.618%   $182.8128   $182.81   $182.80   $182.80  
  Purchase #3 $59.37   11.445%   $66.1649   $66.16   $66.15   $66.20  
  Purchase #4 $214.30   4.561%   $224.0742   $224.07   $224.05   $224.10  
  Purchase #5 $79.89   7.206%   $85.6469   $85.65   $85.65   $85.60  
  Purchase #6 $248.79   5.561%   $262.6252   $262.63   $262.65   $262.60  
  Purchase #7 $183.41   12.436%   $206.2189   $206.22   $206.20   $206.20  
  7 purchase totals = $1,028.92       $1,113.6964   $1,113.69   $1,113.65   $1,113.70