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 $58.82   13.132%   $66.5442   $66.54   $66.55   $66.50  
  Purchase #2 $23.63   6.390%   $25.14   $25.14   $25.15   $25.10  
  Purchase #3 $168.98   5.332%   $177.99   $177.99   $178.00   $178.00  
  Purchase #4 $135.93   8.261%   $147.1592   $147.16   $147.15   $147.20  
  Purchase #5 $90.28   9.544%   $98.8963   $98.90   $98.90   $98.90  
  Purchase #6 $138.75   13.675%   $157.7241   $157.72   $157.70   $157.70  
  Purchase #7 $174.95   10.609%   $193.5104   $193.51   $193.50   $193.50  
  7 purchase totals = $791.34       $866.9642   $866.96   $866.95   $866.90