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 $234.99   7.638%   $252.9385   $252.94   $252.95   $252.90  
  Purchase #2 $119.79   12.105%   $134.2906   $134.29   $134.30   $134.30  
  Purchase #3 $32.95   3.166%   $33.9932   $33.99   $34.00   $34.00  
  Purchase #4 $52.76   4.213%   $54.9828   $54.98   $55.00   $55.00  
  Purchase #5 $93.62   5.809%   $99.0584   $99.06   $99.05   $99.10  
  Purchase #6 $49.99   7.808%   $53.8932   $53.89   $53.90   $53.90  
  Purchase #7 $115.47   6.212%   $122.643   $122.64   $122.65   $122.60  
  7 purchase totals = $699.57       $751.7997   $751.79   $751.85   $751.80