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 $199.99   12.269%   $224.5268   $224.53   $224.55   $224.50  
  Purchase #2 $106.27   9.397%   $116.2562   $116.26   $116.25   $116.30  
  Purchase #3 $28.76   3.102%   $29.6521   $29.65   $29.65   $29.70  
  Purchase #4 $159.98   7.173%   $171.4554   $171.46   $171.45   $171.50  
  Purchase #5 $232.92   13.788%   $265.035   $265.04   $265.05   $265.00  
  Purchase #6 $46.41   13.624%   $52.7329   $52.73   $52.75   $52.70  
  Purchase #7 $174.98   9.808%   $192.142   $192.14   $192.15   $192.10  
  7 purchase totals = $949.31       $1,051.8004   $1,051.81   $1,051.85   $1,051.80