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	$35.61	8.405%	$38.603	$38.60	$38.60	$38.60
Purchase #2	$122.66	9.401%	$134.1913	$134.19	$134.20	$134.20
Purchase #3	$113.68	11.440%	$126.685	$126.69	$126.70	$126.70
Purchase #4	$65.79	10.322%	$72.5808	$72.58	$72.60	$72.60
Purchase #5	$160.75	7.186%	$172.3015	$172.30	$172.30	$172.30
Purchase #6	$35.70	4.741%	$37.3925	$37.39	$37.40	$37.40
Purchase #7	$80.75	12.150%	$90.5611	$90.56	$90.55	$90.60
7 purchase totals =	$614.94		$672.3152	$672.31	$672.35	$672.40