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 $239.26   3.760%   $248.2562   $248.26   $248.25   $248.30  
  Purchase #2 $16.54   6.794%   $17.6637   $17.66   $17.65   $17.70  
  Purchase #3 $58.68   7.442%   $63.047   $63.05   $63.05   $63.00  
  Purchase #4 $110.37   3.114%   $113.8069   $113.81   $113.80   $113.80  
  Purchase #5 $153.66   7.583%   $165.312   $165.31   $165.30   $165.30  
  Purchase #6 $31.46   11.697%   $35.1399   $35.14   $35.15   $35.10  
  Purchase #7 $185.39   4.786%   $194.2628   $194.26   $194.25   $194.30  
  7 purchase totals = $795.36       $837.4885   $837.49   $837.45   $837.50