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	$184.25	4.491%	$192.5247	$192.52	$192.50	$192.50
Purchase #2	$161.53	13.569%	$183.448	$183.45	$183.45	$183.40
Purchase #3	$140.56	9.194%	$153.4831	$153.48	$153.50	$153.50
Purchase #4	$110.56	6.325%	$117.5529	$117.55	$117.55	$117.60
Purchase #5	$102.29	8.649%	$111.1371	$111.14	$111.15	$111.10
Purchase #6	$45.40	12.744%	$51.1858	$51.19	$51.20	$51.20
Purchase #7	$68.81	13.865%	$78.3505	$78.35	$78.35	$78.40
7 purchase totals =	$813.40		$887.6821	$887.68	$887.70	$887.70