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 $54.60   13.611%   $62.0316   $62.03   $62.05   $62.00  
  Purchase #2 $60.49   5.121%   $63.5877   $63.59   $63.60   $63.60  
  Purchase #3 $75.69   13.563%   $85.9558   $85.96   $85.95   $86.00  
  Purchase #4 $88.73   8.148%   $95.9597   $95.96   $95.95   $96.00  
  Purchase #5 $24.49   8.496%   $26.5707   $26.57   $26.55   $26.60  
  Purchase #6 $114.25   4.308%   $119.1719   $119.17   $119.15   $119.20  
  Purchase #7 $193.91   7.728%   $208.8954   $208.90   $208.90   $208.90  
  7 purchase totals = $612.16       $662.1728   $662.18   $662.15   $662.30