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 $48.85   5.200%   $51.3902   $51.39   $51.40   $51.40  
  Purchase #2 $185.33   11.342%   $206.3501   $206.35   $206.35   $206.40  
  Purchase #3 $28.93   11.866%   $32.3628   $32.36   $32.35   $32.40  
  Purchase #4 $225.49   7.219%   $241.7681   $241.77   $241.75   $241.80  
  Purchase #5 $32.39   13.102%   $36.6337   $36.63   $36.65   $36.60  
  Purchase #6 $12.55   13.713%   $14.271   $14.27   $14.25   $14.30  
  Purchase #7 $162.63   12.271%   $182.5863   $182.59   $182.60   $182.60  
  7 purchase totals = $696.17       $765.3622   $765.36   $765.35   $765.50