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	$149.91	6.163%	$159.149	$159.15	$159.15	$159.10
Purchase #2	$169.87	12.192%	$190.5806	$190.58	$190.60	$190.60
Purchase #3	$218.49	3.445%	$226.017	$226.02	$226.00	$226.00
Purchase #4	$47.91	11.747%	$53.538	$53.54	$53.55	$53.50
Purchase #5	$146.47	13.772%	$166.6418	$166.64	$166.65	$166.60
Purchase #6	$81.38	10.208%	$89.6873	$89.69	$89.70	$89.70
Purchase #7	$119.35	3.631%	$123.6836	$123.68	$123.70	$123.70
7 purchase totals =	$933.38		$1,009.2973	$1,009.30	$1,009.35	$1,009.20