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	3.851%	$127.1344	$127.13	$127.15	$127.10
Purchase #2	$139.46	13.754%	$158.6413	$158.64	$158.65	$158.60
Purchase #3	$63.52	12.178%	$71.2555	$71.26	$71.25	$71.30
Purchase #4	$71.53	7.478%	$76.879	$76.88	$76.90	$76.90
Purchase #5	$32.79	9.666%	$35.9595	$35.96	$35.95	$36.00
Purchase #6	$145.62	11.864%	$162.8964	$162.90	$162.90	$162.90
Purchase #7	$248.61	10.671%	$275.1392	$275.14	$275.15	$275.10
7 purchase totals =	$823.95		$907.9053	$907.91	$907.95	$907.90