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	$144.38	8.342%	$156.4242	$156.42	$156.40	$156.40
Purchase #2	$250.91	7.663%	$270.1372	$270.14	$270.15	$270.10
Purchase #3	$34.40	8.482%	$37.3178	$37.32	$37.30	$37.30
Purchase #4	$49.37	3.517%	$51.1063	$51.11	$51.10	$51.10
Purchase #5	$31.52	11.743%	$35.2214	$35.22	$35.20	$35.20
Purchase #6	$181.50	12.842%	$204.8082	$204.81	$204.80	$204.80
Purchase #7	$152.86	13.224%	$173.0742	$173.07	$173.05	$173.10
7 purchase totals =	$844.94		$928.0893	$928.09	$928.00	$928.00