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	$113.39	5.667%	$119.8158	$119.82	$119.80	$119.80
Purchase #2	$22.62	9.243%	$24.7108	$24.71	$24.70	$24.70
Purchase #3	$93.31	7.669%	$100.4659	$100.47	$100.45	$100.50
Purchase #4	$167.71	9.747%	$184.0567	$184.06	$184.05	$184.10
Purchase #5	$10.90	6.632%	$11.6229	$11.62	$11.60	$11.60
Purchase #6	$49.32	10.102%	$54.3023	$54.30	$54.30	$54.30
Purchase #7	$45.72	11.422%	$50.9421	$50.94	$50.95	$50.90
7 purchase totals =	$502.97		$545.9165	$545.92	$545.85	$545.90