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 $212.75   13.114%   $240.65   $240.65   $240.65   $240.70  
  Purchase #2 $29.35   3.513%   $30.3811   $30.38   $30.40   $30.40  
  Purchase #3 $60.69   3.646%   $62.9028   $62.90   $62.90   $62.90  
  Purchase #4 $135.36   3.315%   $139.8472   $139.85   $139.85   $139.80  
  Purchase #5 $208.47   13.141%   $235.865   $235.87   $235.85   $235.90  
  Purchase #6 $53.61   10.769%   $59.3833   $59.38   $59.40   $59.40  
  Purchase #7 $23.42   12.595%   $26.3697   $26.37   $26.35   $26.40  
  7 purchase totals = $723.65       $795.3991   $795.40   $795.40   $795.50