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	$245.85	13.278%	$278.494	$278.49	$278.50	$278.50
Purchase #2	$171.90	3.853%	$178.5233	$178.52	$178.50	$178.50
Purchase #3	$6.82	4.152%	$7.1032	$7.10	$7.10	$7.10
Purchase #4	$194.38	11.177%	$216.1059	$216.11	$216.10	$216.10
Purchase #5	$248.77	4.346%	$259.5815	$259.58	$259.60	$259.60
Purchase #6	$42.54	6.635%	$45.3625	$45.36	$45.35	$45.40
Purchase #7	$95.77	6.814%	$102.2958	$102.30	$102.30	$102.30
7 purchase totals =	$1,006.03		$1,087.4662	$1,087.46	$1,087.45	$1,087.50