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	$16.67	4.173%	$17.3656	$17.37	$17.35	$17.40
Purchase #2	$50.48	3.606%	$52.3003	$52.30	$52.30	$52.30
Purchase #3	$83.86	3.514%	$86.8068	$86.81	$86.80	$86.80
Purchase #4	$104.82	6.698%	$111.8408	$111.84	$111.85	$111.80
Purchase #5	$6.52	7.131%	$6.9849	$6.98	$7.00	$7.00
Purchase #6	$165.67	3.871%	$172.0831	$172.08	$172.10	$172.10
Purchase #7	$223.85	13.104%	$253.1833	$253.18	$253.20	$253.20
7 purchase totals =	$651.87		$700.5648	$700.56	$700.60	$700.60