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	$17.89	3.528%	$18.5212	$18.52	$18.50	$18.50
Purchase #2	$234.31	12.565%	$263.7511	$263.75	$263.75	$263.80
Purchase #3	$119.26	6.113%	$126.5504	$126.55	$126.55	$126.60
Purchase #4	$179.78	4.813%	$188.4328	$188.43	$188.45	$188.40
Purchase #5	$109.74	12.569%	$123.5332	$123.53	$123.55	$123.50
Purchase #6	$244.85	12.851%	$276.3157	$276.32	$276.30	$276.30
Purchase #7	$91.70	11.548%	$102.2895	$102.29	$102.30	$102.30
7 purchase totals =	$997.53		$1,099.3939	$1,099.39	$1,099.40	$1,099.40