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	$226.99	7.723%	$244.5204	$244.52	$244.50	$244.50
Purchase #2	$166.54	12.694%	$187.6806	$187.68	$187.70	$187.70
Purchase #3	$81.44	9.424%	$89.1149	$89.11	$89.10	$89.10
Purchase #4	$219.64	9.235%	$239.9238	$239.92	$239.90	$239.90
Purchase #5	$10.49	3.641%	$10.8719	$10.87	$10.85	$10.90
Purchase #6	$85.56	4.710%	$89.5899	$89.59	$89.60	$89.60
Purchase #7	$247.40	13.622%	$281.1008	$281.10	$281.10	$281.10
7 purchase totals =	$1,038.06		$1,142.8023	$1,142.79	$1,142.75	$1,142.80