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	$144.35	7.808%	$155.6208	$155.62	$155.60	$155.60
Purchase #2	$117.94	4.649%	$123.423	$123.42	$123.40	$123.40
Purchase #3	$9.27	9.508%	$10.1514	$10.15	$10.15	$10.20
Purchase #4	$73.41	5.294%	$77.2963	$77.30	$77.30	$77.30
Purchase #5	$99.75	6.178%	$105.9126	$105.91	$105.90	$105.90
Purchase #6	$123.43	12.207%	$138.4971	$138.50	$138.50	$138.50
Purchase #7	$118.78	3.715%	$123.1927	$123.19	$123.20	$123.20
7 purchase totals =	$686.93		$734.0939	$734.09	$734.05	$734.10