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 $60.96   8.161%   $65.9349   $65.93   $65.95   $65.90  
  Purchase #2 $183.73   8.755%   $199.8156   $199.82   $199.80   $199.80  
  Purchase #3 $74.96   5.519%   $79.097   $79.10   $79.10   $79.10  
  Purchase #4 $211.36   13.306%   $239.4836   $239.48   $239.50   $239.50  
  Purchase #5 $29.39   10.232%   $32.3972   $32.40   $32.40   $32.40  
  Purchase #6 $119.68   12.378%   $134.494   $134.49   $134.50   $134.50  
  Purchase #7 $122.59   12.321%   $137.6943   $137.69   $137.70   $137.70  
  7 purchase totals = $802.67       $888.9166   $888.91   $888.95   $888.90