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	$105.75	13.673%	$120.2092	$120.21	$120.20	$120.20
Purchase #2	$116.50	9.497%	$127.564	$127.56	$127.55	$127.60
Purchase #3	$91.70	4.800%	$96.1016	$96.10	$96.10	$96.10
Purchase #4	$210.70	3.189%	$217.4192	$217.42	$217.40	$217.40
Purchase #5	$149.35	6.689%	$159.34	$159.34	$159.35	$159.30
Purchase #6	$58.80	5.176%	$61.8435	$61.84	$61.85	$61.80
Purchase #7	$13.48	4.231%	$14.0503	$14.05	$14.05	$14.10
7 purchase totals =	$746.28		$796.5278	$796.52	$796.50	$796.50