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 $82.85   3.501%   $85.7506   $85.75   $85.75   $85.80  
  Purchase #2 $168.49   11.724%   $188.2438   $188.24   $188.25   $188.20  
  Purchase #3 $164.49   3.296%   $169.9116   $169.91   $169.90   $169.90  
  Purchase #4 $219.69   6.472%   $233.9083   $233.91   $233.90   $233.90  
  Purchase #5 $22.80   4.296%   $23.7795   $23.78   $23.80   $23.80  
  Purchase #6 $195.49   12.693%   $220.3035   $220.30   $220.30   $220.30  
  Purchase #7 $111.87   3.464%   $115.7452   $115.75   $115.75   $115.70  
  7 purchase totals = $965.68       $1,037.6425   $1,037.64   $1,037.65   $1,037.60