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	$31.39	11.507%	$35.002	$35.00	$35.00	$35.00
Purchase #2	$85.31	4.583%	$89.2198	$89.22	$89.20	$89.20
Purchase #3	$127.68	8.664%	$138.7422	$138.74	$138.75	$138.70
Purchase #4	$220.35	4.797%	$230.9202	$230.92	$230.90	$230.90
Purchase #5	$238.86	3.599%	$247.4566	$247.46	$247.45	$247.50
Purchase #6	$45.85	7.517%	$49.2965	$49.30	$49.30	$49.30
Purchase #7	$241.99	13.747%	$275.2564	$275.26	$275.25	$275.30
7 purchase totals =	$991.43		$1,065.8937	$1,065.90	$1,065.85	$1,065.90