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 $218.46   13.747%   $248.4917   $248.49   $248.50   $248.50  
  Purchase #2 $88.64   10.488%   $97.9366   $97.94   $97.95   $97.90  
  Purchase #3 $235.96   12.786%   $266.1298   $266.13   $266.15   $266.10  
  Purchase #4 $85.88   11.608%   $95.849   $95.85   $95.85   $95.80  
  Purchase #5 $90.50   6.769%   $96.6259   $96.63   $96.65   $96.60  
  Purchase #6 $5.35   13.128%   $6.0523   $6.05   $6.05   $6.10  
  Purchase #7 $154.44   4.335%   $161.135   $161.14   $161.15   $161.10  
  7 purchase totals = $879.23       $972.2203   $972.23   $972.30   $972.10