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	$122.42	3.872%	$127.1601	$127.16	$127.15	$127.20
Purchase #2	$32.29	8.594%	$35.065	$35.07	$35.05	$35.10
Purchase #3	$68.79	8.759%	$74.8153	$74.82	$74.80	$74.80
Purchase #4	$186.35	6.786%	$198.9957	$199.00	$199.00	$199.00
Purchase #5	$83.26	11.121%	$92.5193	$92.52	$92.50	$92.50
Purchase #6	$64.30	10.617%	$71.1267	$71.13	$71.15	$71.10
Purchase #7	$126.29	4.131%	$131.507	$131.51	$131.50	$131.50
7 purchase totals =	$683.70		$731.1891	$731.21	$731.15	$731.20