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 $81.70   5.567%   $86.2482   $86.25   $86.25   $86.20  
  Purchase #2 $191.99   11.341%   $213.7636   $213.76   $213.75   $213.80  
  Purchase #3 $58.49   9.456%   $64.0208   $64.02   $64.00   $64.00  
  Purchase #4 $123.85   11.347%   $137.9033   $137.90   $137.90   $137.90  
  Purchase #5 $58.88   10.837%   $65.2608   $65.26   $65.25   $65.30  
  Purchase #6 $241.35   13.681%   $274.3691   $274.37   $274.35   $274.40  
  Purchase #7 $16.97   11.239%   $18.8773   $18.88   $18.90   $18.90  
  7 purchase totals = $773.23       $860.4431   $860.44   $860.40   $860.50