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 $200.87   3.558%   $208.017   $208.02   $208.00   $208.00  
  Purchase #2 $208.25   5.855%   $220.443   $220.44   $220.45   $220.40  
  Purchase #3 $89.39   8.258%   $96.7718   $96.77   $96.75   $96.80  
  Purchase #4 $17.37   9.405%   $19.0036   $19.00   $19.00   $19.00  
  Purchase #5 $211.84   10.296%   $233.651   $233.65   $233.65   $233.70  
  Purchase #6 $185.49   7.815%   $199.986   $199.99   $200.00   $200.00  
  Purchase #7 $20.95   11.445%   $23.3477   $23.35   $23.35   $23.30  
  7 purchase totals = $934.16       $1,001.2201   $1,001.22   $1,001.20   $1,001.20