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	$10.91	8.103%	$11.794	$11.79	$11.80	$11.80
Purchase #2	$162.35	6.457%	$172.8329	$172.83	$172.85	$172.80
Purchase #3	$35.58	13.851%	$40.5082	$40.51	$40.50	$40.50
Purchase #4	$119.95	5.558%	$126.6168	$126.62	$126.60	$126.60
Purchase #5	$226.98	7.302%	$243.5541	$243.55	$243.55	$243.60
Purchase #6	$181.42	3.840%	$188.3865	$188.39	$188.40	$188.40
Purchase #7	$57.63	6.368%	$61.2999	$61.30	$61.30	$61.30
7 purchase totals =	$794.82		$844.9924	$844.99	$845.00	$845.00