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	$19.68	8.617%	$21.3758	$21.38	$21.40	$21.40
Purchase #2	$71.51	10.237%	$78.8305	$78.83	$78.85	$78.80
Purchase #3	$56.94	5.230%	$59.918	$59.92	$59.90	$59.90
Purchase #4	$172.61	8.589%	$187.4355	$187.44	$187.45	$187.40
Purchase #5	$191.66	7.261%	$205.5764	$205.58	$205.60	$205.60
Purchase #6	$116.35	6.848%	$124.3176	$124.32	$124.30	$124.30
Purchase #7	$244.79	5.380%	$257.9597	$257.96	$257.95	$258.00
7 purchase totals =	$873.54		$935.4135	$935.43	$935.45	$935.40