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	$183.90	13.176%	$208.1307	$208.13	$208.15	$208.10
Purchase #2	$206.59	11.693%	$230.7466	$230.75	$230.75	$230.70
Purchase #3	$52.47	11.782%	$58.652	$58.65	$58.65	$58.70
Purchase #4	$56.27	8.747%	$61.1919	$61.19	$61.20	$61.20
Purchase #5	$231.91	13.544%	$263.3199	$263.32	$263.30	$263.30
Purchase #6	$100.74	10.515%	$111.3328	$111.33	$111.35	$111.30
Purchase #7	$156.52	6.585%	$166.8268	$166.83	$166.85	$166.80
7 purchase totals =	$988.40		$1,100.2007	$1,100.20	$1,100.25	$1,100.10