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	$243.31	11.436%	$271.1349	$271.13	$271.15	$271.10
Purchase #2	$78.53	13.629%	$89.2329	$89.23	$89.25	$89.20
Purchase #3	$58.67	6.273%	$62.3504	$62.35	$62.35	$62.40
Purchase #4	$241.63	8.210%	$261.4678	$261.47	$261.45	$261.50
Purchase #5	$191.65	11.512%	$213.7127	$213.71	$213.70	$213.70
Purchase #6	$45.36	9.158%	$49.5141	$49.51	$49.50	$49.50
Purchase #7	$123.47	3.384%	$127.6482	$127.65	$127.65	$127.60
7 purchase totals =	$982.62		$1,075.0610	$1,075.05	$1,075.05	$1,075.00