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	$70.33	13.691%	$79.9589	$79.96	$79.95	$80.00
Purchase #2	$225.94	11.607%	$252.1649	$252.16	$252.15	$252.20
Purchase #3	$86.36	4.679%	$90.4008	$90.40	$90.40	$90.40
Purchase #4	$172.32	11.323%	$191.8318	$191.83	$191.85	$191.80
Purchase #5	$145.59	6.129%	$154.5132	$154.51	$154.50	$154.50
Purchase #6	$103.37	8.288%	$111.9373	$111.94	$111.95	$111.90
Purchase #7	$118.59	9.853%	$130.2747	$130.27	$130.25	$130.30
7 purchase totals =	$922.50		$1,011.0816	$1,011.07	$1,011.05	$1,011.10