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	$214.64	13.108%	$242.775	$242.78	$242.80	$242.80
Purchase #2	$37.64	13.872%	$42.8614	$42.86	$42.85	$42.90
Purchase #3	$212.26	10.148%	$233.8001	$233.80	$233.80	$233.80
Purchase #4	$103.67	12.542%	$116.6723	$116.67	$116.65	$116.70
Purchase #5	$71.58	8.313%	$77.5304	$77.53	$77.55	$77.50
Purchase #6	$14.28	5.479%	$15.0624	$15.06	$15.05	$15.10
Purchase #7	$88.49	3.311%	$91.4199	$91.42	$91.40	$91.40
7 purchase totals =	$742.56		$820.1215	$820.12	$820.10	$820.20