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	$105.51	5.321%	$111.1242	$111.12	$111.10	$111.10
Purchase #2	$21.54	6.425%	$22.9239	$22.92	$22.90	$22.90
Purchase #3	$129.90	13.559%	$147.5131	$147.51	$147.50	$147.50
Purchase #4	$68.31	11.260%	$76.0017	$76.00	$76.00	$76.00
Purchase #5	$39.71	9.292%	$43.3999	$43.40	$43.40	$43.40
Purchase #6	$37.64	7.743%	$40.5545	$40.55	$40.55	$40.60
Purchase #7	$55.76	10.429%	$61.5752	$61.58	$61.60	$61.60
7 purchase totals =	$458.37		$503.0925	$503.08	$503.05	$503.10