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	$71.88	8.720%	$78.1479	$78.15	$78.15	$78.10
Purchase #2	$241.81	5.563%	$255.2619	$255.26	$255.25	$255.30
Purchase #3	$90.78	9.843%	$99.7155	$99.72	$99.70	$99.70
Purchase #4	$21.39	11.680%	$23.8884	$23.89	$23.90	$23.90
Purchase #5	$170.29	3.723%	$176.6299	$176.63	$176.65	$176.60
Purchase #6	$50.52	11.704%	$56.4329	$56.43	$56.45	$56.40
Purchase #7	$195.79	3.658%	$202.952	$202.95	$202.95	$203.00
7 purchase totals =	$842.46		$893.0285	$893.03	$893.05	$893.00