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	$52.51	7.256%	$56.3201	$56.32	$56.30	$56.30
Purchase #2	$129.95	13.451%	$147.4296	$147.43	$147.45	$147.40
Purchase #3	$188.65	4.271%	$196.7072	$196.71	$196.70	$196.70
Purchase #4	$9.89	7.396%	$10.6215	$10.62	$10.60	$10.60
Purchase #5	$110.34	8.377%	$119.5832	$119.58	$119.60	$119.60
Purchase #6	$16.83	9.238%	$18.3848	$18.38	$18.40	$18.40
Purchase #7	$91.94	4.187%	$95.7895	$95.79	$95.80	$95.80
7 purchase totals =	$600.11		$644.8359	$644.83	$644.85	$644.80