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	$38.60	10.317%	$42.5824	$42.58	$42.60	$42.60
Purchase #2	$235.64	11.124%	$261.8526	$261.85	$261.85	$261.90
Purchase #3	$19.92	7.683%	$21.4505	$21.45	$21.45	$21.50
Purchase #4	$196.87	13.606%	$223.6561	$223.66	$223.65	$223.70
Purchase #5	$28.31	5.441%	$29.8503	$29.85	$29.85	$29.90
Purchase #6	$188.73	12.243%	$211.8362	$211.84	$211.85	$211.80
Purchase #7	$165.45	8.186%	$178.9937	$178.99	$179.00	$179.00
7 purchase totals =	$873.52		$970.2218	$970.22	$970.25	$970.40