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 $134.72   8.383%   $146.0136   $146.01   $146.00   $146.00  
  Purchase #2 $33.76   3.572%   $34.9659   $34.97   $34.95   $35.00  
  Purchase #3 $111.97   4.105%   $116.5664   $116.57   $116.55   $116.60  
  Purchase #4 $82.69   12.636%   $93.1387   $93.14   $93.15   $93.10  
  Purchase #5 $110.90   10.145%   $122.1508   $122.15   $122.15   $122.20  
  Purchase #6 $5.71   5.385%   $6.0175   $6.02   $6.00   $6.00  
  Purchase #7 $156.58   4.794%   $164.0864   $164.09   $164.10   $164.10  
  7 purchase totals = $636.33       $682.9393   $682.95   $682.90   $683.00