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	$121.32	13.605%	$137.8256	$137.83	$137.85	$137.80
Purchase #2	$20.36	3.448%	$21.062	$21.06	$21.05	$21.10
Purchase #3	$166.90	4.532%	$174.4639	$174.46	$174.45	$174.50
Purchase #4	$233.68	10.259%	$257.6532	$257.65	$257.65	$257.70
Purchase #5	$37.77	13.294%	$42.7911	$42.79	$42.80	$42.80
Purchase #6	$196.94	9.482%	$215.6139	$215.61	$215.60	$215.60
Purchase #7	$50.26	9.832%	$55.2016	$55.20	$55.20	$55.20
7 purchase totals =	$827.23		$904.6113	$904.60	$904.60	$904.70