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	$236.81	7.709%	$255.0657	$255.07	$255.05	$255.10
Purchase #2	$243.64	4.368%	$254.2822	$254.28	$254.30	$254.30
Purchase #3	$15.46	12.649%	$17.4155	$17.42	$17.40	$17.40
Purchase #4	$111.33	10.536%	$123.0597	$123.06	$123.05	$123.10
Purchase #5	$111.47	13.153%	$126.1316	$126.13	$126.15	$126.10
Purchase #6	$65.69	5.700%	$69.4343	$69.43	$69.45	$69.40
Purchase #7	$226.62	12.505%	$254.9588	$254.96	$254.95	$255.00
7 purchase totals =	$1,011.02		$1,100.3478	$1,100.35	$1,100.35	$1,100.40