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 $92.58   4.131%   $96.4045   $96.40   $96.40   $96.40  
  Purchase #2 $185.41   8.592%   $201.3404   $201.34   $201.35   $201.30  
  Purchase #3 $238.31   7.414%   $255.9783   $255.98   $256.00   $256.00  
  Purchase #4 $64.99   3.191%   $67.0638   $67.06   $67.05   $67.10  
  Purchase #5 $239.25   5.664%   $252.8011   $252.80   $252.80   $252.80  
  Purchase #6 $144.88   7.290%   $155.4418   $155.44   $155.45   $155.40  
  Purchase #7 $239.87   3.746%   $248.8555   $248.86   $248.85   $248.90  
  7 purchase totals = $1,205.29       $1,277.8854   $1,277.88   $1,277.90   $1,277.90