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 $86.47   13.281%   $97.9541   $97.95   $97.95   $98.00  
  Purchase #2 $77.63   7.245%   $83.2543   $83.25   $83.25   $83.30  
  Purchase #3 $136.65   3.176%   $140.99   $140.99   $141.00   $141.00  
  Purchase #4 $201.47   6.567%   $214.7005   $214.70   $214.70   $214.70  
  Purchase #5 $199.45   4.542%   $208.509   $208.51   $208.50   $208.50  
  Purchase #6 $166.34   7.411%   $178.6675   $178.67   $178.65   $178.70  
  Purchase #7 $45.67   12.582%   $51.4162   $51.42   $51.40   $51.40  
  7 purchase totals = $913.68       $975.4916   $975.49   $975.45   $975.60