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	$20.70	6.619%	$22.0701	$22.07	$22.05	$22.10
Purchase #2	$82.33	7.680%	$88.6529	$88.65	$88.65	$88.70
Purchase #3	$90.66	9.540%	$99.309	$99.31	$99.30	$99.30
Purchase #4	$101.25	8.198%	$109.5505	$109.55	$109.55	$109.60
Purchase #5	$32.98	3.276%	$34.0604	$34.06	$34.05	$34.10
Purchase #6	$90.52	4.502%	$94.5952	$94.60	$94.60	$94.60
Purchase #7	$66.95	11.145%	$74.4116	$74.41	$74.40	$74.40
7 purchase totals =	$485.39		$522.6497	$522.65	$522.60	$522.80