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	$204.71	6.430%	$217.8729	$217.87	$217.85	$217.90
Purchase #2	$79.62	12.776%	$89.7923	$89.79	$89.80	$89.80
Purchase #3	$203.76	13.154%	$230.5626	$230.56	$230.55	$230.60
Purchase #4	$126.32	6.430%	$134.4424	$134.44	$134.45	$134.40
Purchase #5	$110.40	12.868%	$124.6063	$124.61	$124.60	$124.60
Purchase #6	$164.30	4.783%	$172.1585	$172.16	$172.15	$172.20
Purchase #7	$21.80	13.443%	$24.7306	$24.73	$24.75	$24.70
7 purchase totals =	$910.91		$994.1656	$994.16	$994.15	$994.20