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	$230.45	5.799%	$243.8138	$243.81	$243.80	$243.80
Purchase #2	$235.97	9.613%	$258.6538	$258.65	$258.65	$258.70
Purchase #3	$169.53	13.112%	$191.7588	$191.76	$191.75	$191.80
Purchase #4	$103.87	8.390%	$112.5847	$112.58	$112.60	$112.60
Purchase #5	$226.54	12.274%	$254.3455	$254.35	$254.35	$254.30
Purchase #6	$80.28	12.623%	$90.4137	$90.41	$90.40	$90.40
Purchase #7	$10.97	13.820%	$12.4861	$12.49	$12.50	$12.50
7 purchase totals =	$1,057.61		$1,164.0564	$1,164.05	$1,164.05	$1,164.10