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	$82.46	9.609%	$90.3836	$90.38	$90.40	$90.40
Purchase #2	$12.79	12.520%	$14.3913	$14.39	$14.40	$14.40
Purchase #3	$53.40	7.621%	$57.4696	$57.47	$57.45	$57.50
Purchase #4	$87.67	4.174%	$91.3293	$91.33	$91.35	$91.30
Purchase #5	$220.79	8.529%	$239.6212	$239.62	$239.60	$239.60
Purchase #6	$69.98	3.474%	$72.4111	$72.41	$72.40	$72.40
Purchase #7	$157.30	13.384%	$178.353	$178.35	$178.35	$178.40
7 purchase totals =	$684.39		$743.9591	$743.95	$743.95	$744.00