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	$173.83	4.197%	$181.1256	$181.13	$181.15	$181.10
Purchase #2	$139.76	13.714%	$158.9267	$158.93	$158.95	$158.90
Purchase #3	$69.73	12.568%	$78.4937	$78.49	$78.50	$78.50
Purchase #4	$205.91	10.517%	$227.5656	$227.57	$227.55	$227.60
Purchase #5	$50.60	11.842%	$56.5921	$56.59	$56.60	$56.60
Purchase #6	$163.81	3.346%	$169.2911	$169.29	$169.30	$169.30
Purchase #7	$108.56	9.728%	$119.1207	$119.12	$119.10	$119.10
7 purchase totals =	$912.20		$991.1155	$991.12	$991.15	$991.10