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	$16.97	9.168%	$18.5258	$18.53	$18.55	$18.50
Purchase #2	$17.49	6.354%	$18.6013	$18.60	$18.60	$18.60
Purchase #3	$105.85	5.702%	$111.8856	$111.89	$111.90	$111.90
Purchase #4	$110.65	3.396%	$114.4077	$114.41	$114.40	$114.40
Purchase #5	$119.94	13.400%	$136.012	$136.01	$136.00	$136.00
Purchase #6	$194.89	5.495%	$205.5992	$205.60	$205.60	$205.60
Purchase #7	$55.52	10.114%	$61.1353	$61.14	$61.15	$61.10
7 purchase totals =	$621.31		$666.1669	$666.18	$666.20	$666.10