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	$109.83	9.322%	$120.0684	$120.07	$120.05	$120.10
Purchase #2	$106.64	4.337%	$111.265	$111.27	$111.25	$111.30
Purchase #3	$33.58	6.536%	$35.7748	$35.77	$35.75	$35.80
Purchase #4	$140.40	4.412%	$146.5944	$146.59	$146.60	$146.60
Purchase #5	$190.52	12.312%	$213.9768	$213.98	$214.00	$214.00
Purchase #6	$125.42	3.353%	$129.6253	$129.63	$129.65	$129.60
Purchase #7	$38.36	12.156%	$43.023	$43.02	$43.00	$43.00
7 purchase totals =	$744.75		$800.3277	$800.33	$800.30	$800.40