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	$74.59	3.658%	$77.3185	$77.32	$77.30	$77.30
Purchase #2	$70.93	10.783%	$78.5784	$78.58	$78.60	$78.60
Purchase #3	$242.55	13.215%	$274.603	$274.60	$274.60	$274.60
Purchase #4	$10.98	6.662%	$11.7115	$11.71	$11.70	$11.70
Purchase #5	$144.89	9.165%	$158.1692	$158.17	$158.15	$158.20
Purchase #6	$72.78	6.360%	$77.4088	$77.41	$77.40	$77.40
Purchase #7	$248.26	4.230%	$258.7614	$258.76	$258.75	$258.80
7 purchase totals =	$864.98		$936.5508	$936.55	$936.50	$936.60