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	$14.30	6.413%	$15.2171	$15.22	$15.20	$15.20
Purchase #2	$89.42	10.172%	$98.5158	$98.52	$98.50	$98.50
Purchase #3	$12.80	8.152%	$13.8435	$13.84	$13.85	$13.80
Purchase #4	$234.82	9.566%	$257.2829	$257.28	$257.30	$257.30
Purchase #5	$72.28	10.450%	$79.8333	$79.83	$79.85	$79.80
Purchase #6	$204.96	9.847%	$225.1424	$225.14	$225.15	$225.10
Purchase #7	$98.94	12.548%	$111.355	$111.36	$111.35	$111.40
7 purchase totals =	$727.52		$801.1900	$801.19	$801.20	$801.10