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	$167.38	3.242%	$172.8065	$172.81	$172.80	$172.80
Purchase #2	$33.50	3.767%	$34.7619	$34.76	$34.75	$34.80
Purchase #3	$124.29	10.471%	$137.3044	$137.30	$137.30	$137.30
Purchase #4	$221.51	11.451%	$246.8751	$246.88	$246.90	$246.90
Purchase #5	$40.37	13.643%	$45.8777	$45.88	$45.90	$45.90
Purchase #6	$194.66	13.560%	$221.0559	$221.06	$221.05	$221.10
Purchase #7	$20.25	5.558%	$21.3755	$21.38	$21.40	$21.40
7 purchase totals =	$801.96		$880.0570	$880.07	$880.10	$880.20