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	$49.65	9.861%	$54.546	$54.55	$54.55	$54.50
Purchase #2	$17.82	9.150%	$19.4505	$19.45	$19.45	$19.50
Purchase #3	$225.60	13.117%	$255.192	$255.19	$255.20	$255.20
Purchase #4	$213.55	4.624%	$223.4246	$223.42	$223.40	$223.40
Purchase #5	$26.44	10.517%	$29.2207	$29.22	$29.20	$29.20
Purchase #6	$209.75	3.747%	$217.6093	$217.61	$217.60	$217.60
Purchase #7	$38.40	10.716%	$42.5149	$42.51	$42.50	$42.50
7 purchase totals =	$781.21		$841.9580	$841.95	$841.90	$841.90