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	$156.25	6.524%	$166.4438	$166.44	$166.45	$166.40
Purchase #2	$142.56	12.809%	$160.8205	$160.82	$160.80	$160.80
Purchase #3	$246.39	13.590%	$279.8744	$279.87	$279.85	$279.90
Purchase #4	$102.62	13.619%	$116.5958	$116.60	$116.60	$116.60
Purchase #5	$149.36	7.859%	$161.0982	$161.10	$161.10	$161.10
Purchase #6	$97.96	10.789%	$108.5289	$108.53	$108.55	$108.50
Purchase #7	$106.56	4.640%	$111.5044	$111.50	$111.50	$111.50
7 purchase totals =	$1,001.70		$1,104.8660	$1,104.86	$1,104.85	$1,104.80