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 $192.69   11.451%   $214.7549   $214.75   $214.75   $214.80  
  Purchase #2 $176.66   4.179%   $184.0426   $184.04   $184.05   $184.00  
  Purchase #3 $55.68   5.795%   $58.9067   $58.91   $58.90   $58.90  
  Purchase #4 $199.39   11.340%   $222.0008   $222.00   $222.00   $222.00  
  Purchase #5 $70.60   5.105%   $74.2041   $74.20   $74.20   $74.20  
  Purchase #6 $139.56   6.623%   $148.8031   $148.80   $148.80   $148.80  
  Purchase #7 $44.72   5.675%   $47.2579   $47.26   $47.25   $47.30  
  7 purchase totals = $879.30       $949.9701   $949.96   $949.95   $950.00