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 $67.87   12.628%   $76.4406   $76.44   $76.45   $76.40  
  Purchase #2 $169.42   9.858%   $186.1214   $186.12   $186.10   $186.10  
  Purchase #3 $250.44   13.164%   $283.4079   $283.41   $283.40   $283.40  
  Purchase #4 $35.80   13.772%   $40.7304   $40.73   $40.75   $40.70  
  Purchase #5 $97.98   3.169%   $101.085   $101.09   $101.10   $101.10  
  Purchase #6 $219.92   5.397%   $231.7891   $231.79   $231.80   $231.80  
  Purchase #7 $95.45   6.540%   $101.6924   $101.69   $101.70   $101.70  
  7 purchase totals = $936.88       $1,021.2668   $1,021.27   $1,021.30   $1,021.20