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	$113.79	8.721%	$123.7136	$123.71	$123.70	$123.70
Purchase #2	$149.73	11.123%	$166.3845	$166.38	$166.40	$166.40
Purchase #3	$84.59	6.304%	$89.9226	$89.92	$89.90	$89.90
Purchase #4	$97.41	11.245%	$108.3638	$108.36	$108.35	$108.40
Purchase #5	$235.30	13.295%	$266.5831	$266.58	$266.60	$266.60
Purchase #6	$65.80	3.592%	$68.1635	$68.16	$68.15	$68.20
Purchase #7	$106.79	4.770%	$111.8839	$111.88	$111.90	$111.90
7 purchase totals =	$853.41		$935.0150	$934.99	$935.00	$935.10