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	$17.29	4.671%	$18.0976	$18.10	$18.10	$18.10
Purchase #2	$85.89	9.725%	$94.2428	$94.24	$94.25	$94.20
Purchase #3	$196.89	11.730%	$219.9852	$219.99	$220.00	$220.00
Purchase #4	$78.30	13.848%	$89.143	$89.14	$89.15	$89.10
Purchase #5	$129.82	6.767%	$138.6049	$138.60	$138.60	$138.60
Purchase #6	$6.28	8.533%	$6.8159	$6.82	$6.80	$6.80
Purchase #7	$153.75	13.708%	$174.8261	$174.83	$174.85	$174.80
7 purchase totals =	$668.22		$741.7155	$741.72	$741.75	$741.60