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 $208.28   11.624%   $232.4905   $232.49   $232.50   $232.50  
  Purchase #2 $241.26   8.448%   $261.6416   $261.64   $261.65   $261.60  
  Purchase #3 $33.98   5.678%   $35.9094   $35.91   $35.90   $35.90  
  Purchase #4 $76.77   5.865%   $81.2726   $81.27   $81.25   $81.30  
  Purchase #5 $190.82   4.788%   $199.9565   $199.96   $199.95   $200.00  
  Purchase #6 $205.74   9.858%   $226.0218   $226.02   $226.00   $226.00  
  Purchase #7 $18.47   13.126%   $20.8944   $20.89   $20.90   $20.90  
  7 purchase totals = $975.32       $1,058.1868   $1,058.18   $1,058.15   $1,058.20