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	$27.29	9.688%	$29.9339	$29.93	$29.95	$29.90
Purchase #2	$169.59	13.671%	$192.7746	$192.77	$192.75	$192.80
Purchase #3	$216.32	5.116%	$227.3869	$227.39	$227.40	$227.40
Purchase #4	$77.54	6.683%	$82.722	$82.72	$82.70	$82.70
Purchase #5	$67.31	4.579%	$70.3921	$70.39	$70.40	$70.40
Purchase #6	$83.93	9.160%	$91.618	$91.62	$91.60	$91.60
Purchase #7	$90.45	3.599%	$93.7053	$93.71	$93.70	$93.70
7 purchase totals =	$732.43		$788.5328	$788.53	$788.50	$788.50