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	$104.38	6.606%	$111.2753	$111.28	$111.30	$111.30
Purchase #2	$48.47	12.632%	$54.5927	$54.59	$54.60	$54.60
Purchase #3	$170.92	11.767%	$191.0322	$191.03	$191.05	$191.00
Purchase #4	$247.87	10.743%	$274.4987	$274.50	$274.50	$274.50
Purchase #5	$132.32	12.150%	$148.3969	$148.40	$148.40	$148.40
Purchase #6	$88.64	8.669%	$96.3242	$96.32	$96.30	$96.30
Purchase #7	$14.37	5.709%	$15.1904	$15.19	$15.20	$15.20
7 purchase totals =	$806.97		$891.3104	$891.31	$891.35	$891.30