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	$10.41	3.559%	$10.7805	$10.78	$10.80	$10.80
Purchase #2	$83.65	8.827%	$91.0338	$91.03	$91.05	$91.00
Purchase #3	$44.80	11.382%	$49.8991	$49.90	$49.90	$49.90
Purchase #4	$217.51	11.581%	$242.6998	$242.70	$242.70	$242.70
Purchase #5	$243.41	10.325%	$268.5421	$268.54	$268.55	$268.50
Purchase #6	$48.68	12.673%	$54.8492	$54.85	$54.85	$54.80
Purchase #7	$54.83	7.818%	$59.1166	$59.12	$59.10	$59.10
7 purchase totals =	$703.29		$776.9211	$776.92	$776.95	$776.80