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 $44.96   11.104%   $49.9524   $49.95   $49.95   $50.00  
  Purchase #2 $248.77   6.634%   $265.2734   $265.27   $265.25   $265.30  
  Purchase #3 $23.58   13.232%   $26.7001   $26.70   $26.70   $26.70  
  Purchase #4 $62.66   5.337%   $66.0042   $66.00   $66.00   $66.00  
  Purchase #5 $72.86   10.493%   $80.5052   $80.51   $80.50   $80.50  
  Purchase #6 $127.39   5.271%   $134.1047   $134.10   $134.10   $134.10  
  Purchase #7 $163.92   6.651%   $174.8223   $174.82   $174.80   $174.80  
  7 purchase totals = $744.14       $797.3623   $797.35   $797.30   $797.40