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	$144.55	5.735%	$152.8399	$152.84	$152.85	$152.80
Purchase #2	$101.45	9.815%	$111.4073	$111.41	$111.40	$111.40
Purchase #3	$230.77	4.794%	$241.8331	$241.83	$241.85	$241.80
Purchase #4	$50.49	8.176%	$54.6181	$54.62	$54.60	$54.60
Purchase #5	$176.37	4.598%	$184.4795	$184.48	$184.50	$184.50
Purchase #6	$123.44	7.479%	$132.6721	$132.67	$132.65	$132.70
Purchase #7	$84.42	13.735%	$96.0151	$96.02	$96.00	$96.00
7 purchase totals =	$911.49		$973.8651	$973.87	$973.85	$973.80