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 $22.93   3.481%   $23.7282   $23.73   $23.75   $23.70  
  Purchase #2 $172.48   12.297%   $193.6899   $193.69   $193.70   $193.70  
  Purchase #3 $228.94   8.495%   $248.3885   $248.39   $248.40   $248.40  
  Purchase #4 $139.97   6.404%   $148.9337   $148.93   $148.95   $148.90  
  Purchase #5 $232.71   8.370%   $252.1878   $252.19   $252.20   $252.20  
  Purchase #6 $224.36   13.327%   $254.2605   $254.26   $254.25   $254.30  
  Purchase #7 $86.82   10.657%   $96.0724   $96.07   $96.05   $96.10  
  7 purchase totals = $1,108.21       $1,217.2610   $1,217.26   $1,217.30   $1,217.30