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 $124.49   13.472%   $141.2613   $141.26   $141.25   $141.30  
  Purchase #2 $108.83   5.119%   $114.401   $114.40   $114.40   $114.40  
  Purchase #3 $12.79   5.370%   $13.4768   $13.48   $13.50   $13.50  
  Purchase #4 $30.31   13.358%   $34.3588   $34.36   $34.35   $34.40  
  Purchase #5 $168.29   11.270%   $187.2563   $187.26   $187.25   $187.30  
  Purchase #6 $207.25   8.507%   $224.8808   $224.88   $224.90   $224.90  
  Purchase #7 $13.39   13.151%   $15.1509   $15.15   $15.15   $15.20  
  7 purchase totals = $665.35       $730.7859   $730.79   $730.80   $731.00