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	$17.72	9.265%	$19.3618	$19.36	$19.35	$19.40
Purchase #2	$56.84	10.156%	$62.6127	$62.61	$62.60	$62.60
Purchase #3	$92.52	11.673%	$103.3199	$103.32	$103.30	$103.30
Purchase #4	$48.55	13.102%	$54.911	$54.91	$54.90	$54.90
Purchase #5	$142.91	10.646%	$158.1242	$158.12	$158.10	$158.10
Purchase #6	$164.98	13.697%	$187.5773	$187.58	$187.60	$187.60
Purchase #7	$94.57	10.290%	$104.3013	$104.30	$104.30	$104.30
7 purchase totals =	$618.09		$690.2082	$690.20	$690.15	$690.20