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	$229.42	4.638%	$240.0605	$240.06	$240.05	$240.10
Purchase #2	$54.48	6.123%	$57.8158	$57.82	$57.80	$57.80
Purchase #3	$80.42	11.159%	$89.3941	$89.39	$89.40	$89.40
Purchase #4	$8.39	11.861%	$9.3851	$9.39	$9.40	$9.40
Purchase #5	$120.53	10.782%	$133.5255	$133.53	$133.55	$133.50
Purchase #6	$237.45	7.214%	$254.5796	$254.58	$254.60	$254.60
Purchase #7	$49.66	9.773%	$54.5133	$54.51	$54.50	$54.50
7 purchase totals =	$780.35		$839.2739	$839.28	$839.30	$839.30