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 $46.95   13.541%   $53.3075   $53.31   $53.30   $53.30  
  Purchase #2 $216.97   11.739%   $242.4401   $242.44   $242.45   $242.40  
  Purchase #3 $159.37   13.765%   $181.3073   $181.31   $181.30   $181.30  
  Purchase #4 $249.54   11.552%   $278.3669   $278.37   $278.35   $278.40  
  Purchase #5 $102.96   10.105%   $113.3641   $113.36   $113.35   $113.40  
  Purchase #6 $158.87   12.326%   $178.4523   $178.45   $178.45   $178.50  
  Purchase #7 $234.25   13.770%   $266.5062   $266.51   $266.50   $266.50  
  7 purchase totals = $1,168.91       $1,313.7444   $1,313.75   $1,313.70   $1,313.80