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	$17.50	6.667%	$18.6667	$18.67	$18.65	$18.70
Purchase #2	$151.29	6.575%	$161.2373	$161.24	$161.25	$161.20
Purchase #3	$87.28	3.874%	$90.6612	$90.66	$90.65	$90.70
Purchase #4	$101.52	9.478%	$111.1421	$111.14	$111.15	$111.10
Purchase #5	$111.79	12.338%	$125.5827	$125.58	$125.60	$125.60
Purchase #6	$5.89	3.778%	$6.1125	$6.11	$6.10	$6.10
Purchase #7	$129.49	10.331%	$142.8676	$142.87	$142.85	$142.90
7 purchase totals =	$604.76		$656.2701	$656.27	$656.25	$656.30