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	$81.27	5.853%	$86.0267	$86.03	$86.05	$86.00
Purchase #2	$102.84	12.834%	$116.0385	$116.04	$116.05	$116.00
Purchase #3	$101.55	7.849%	$109.5207	$109.52	$109.50	$109.50
Purchase #4	$107.32	6.487%	$114.2818	$114.28	$114.30	$114.30
Purchase #5	$23.37	10.526%	$25.8299	$25.83	$25.85	$25.80
Purchase #6	$110.83	5.213%	$116.6076	$116.61	$116.60	$116.60
Purchase #7	$37.28	13.845%	$42.4414	$42.44	$42.45	$42.40
7 purchase totals =	$564.46		$610.7466	$610.75	$610.80	$610.60