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	$74.45	5.432%	$78.4941	$78.49	$78.50	$78.50
Purchase #2	$49.87	6.471%	$53.0971	$53.10	$53.10	$53.10
Purchase #3	$130.79	11.866%	$146.3095	$146.31	$146.30	$146.30
Purchase #4	$36.62	9.591%	$40.1322	$40.13	$40.15	$40.10
Purchase #5	$200.89	6.594%	$214.1367	$214.14	$214.15	$214.10
Purchase #6	$138.47	5.389%	$145.9321	$145.93	$145.95	$145.90
Purchase #7	$97.60	6.399%	$103.8454	$103.85	$103.85	$103.80
7 purchase totals =	$728.69		$781.9471	$781.95	$782.00	$781.80