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	$108.35	12.806%	$122.2253	$122.23	$122.25	$122.20
Purchase #2	$43.63	3.443%	$45.1322	$45.13	$45.15	$45.10
Purchase #3	$27.54	13.268%	$31.194	$31.19	$31.20	$31.20
Purchase #4	$102.32	9.324%	$111.8603	$111.86	$111.85	$111.90
Purchase #5	$185.90	7.450%	$199.7496	$199.75	$199.75	$199.70
Purchase #6	$10.42	12.534%	$11.726	$11.73	$11.75	$11.70
Purchase #7	$52.99	11.450%	$59.0574	$59.06	$59.05	$59.10
7 purchase totals =	$531.15		$580.9448	$580.95	$581.00	$580.90