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	$204.36	4.599%	$213.7585	$213.76	$213.75	$213.80
Purchase #2	$46.43	12.503%	$52.2351	$52.24	$52.25	$52.20
Purchase #3	$47.94	9.239%	$52.3692	$52.37	$52.35	$52.40
Purchase #4	$226.47	6.444%	$241.0637	$241.06	$241.05	$241.10
Purchase #5	$111.44	13.502%	$126.4866	$126.49	$126.50	$126.50
Purchase #6	$245.60	11.420%	$273.6475	$273.65	$273.65	$273.60
Purchase #7	$54.39	8.759%	$59.154	$59.15	$59.15	$59.20
7 purchase totals =	$936.63		$1,018.7146	$1,018.72	$1,018.70	$1,018.80