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 $62.69   5.719%   $66.2752   $66.28   $66.30   $66.30  
  Purchase #2 $85.51   4.224%   $89.1219   $89.12   $89.10   $89.10  
  Purchase #3 $53.39   5.525%   $56.3398   $56.34   $56.35   $56.30  
  Purchase #4 $163.25   10.173%   $179.8574   $179.86   $179.85   $179.90  
  Purchase #5 $144.86   8.853%   $157.6845   $157.68   $157.70   $157.70  
  Purchase #6 $196.44   5.854%   $207.9396   $207.94   $207.95   $207.90  
  Purchase #7 $91.77   7.624%   $98.7665   $98.77   $98.75   $98.80  
  7 purchase totals = $797.91       $855.9849   $855.99   $856.00   $856.00