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 $216.45   6.146%   $229.753   $229.75   $229.75   $229.80  
  Purchase #2 $64.81   11.856%   $72.4939   $72.49   $72.50   $72.50  
  Purchase #3 $17.54   11.660%   $19.5852   $19.59   $19.60   $19.60  
  Purchase #4 $129.77   8.350%   $140.6058   $140.61   $140.60   $140.60  
  Purchase #5 $49.60   11.706%   $55.4062   $55.41   $55.40   $55.40  
  Purchase #6 $239.97   3.722%   $248.9017   $248.90   $248.90   $248.90  
  Purchase #7 $208.93   9.221%   $228.1954   $228.20   $228.20   $228.20  
  7 purchase totals = $927.07       $994.9412   $994.95   $994.95   $995.00