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	$37.80	6.337%	$40.1954	$40.20	$40.20	$40.20
Purchase #2	$139.83	11.792%	$156.3188	$156.32	$156.30	$156.30
Purchase #3	$42.84	6.465%	$45.6096	$45.61	$45.60	$45.60
Purchase #4	$134.29	7.273%	$144.0569	$144.06	$144.05	$144.10
Purchase #5	$208.41	8.810%	$226.7709	$226.77	$226.75	$226.80
Purchase #6	$162.94	13.408%	$184.787	$184.79	$184.80	$184.80
Purchase #7	$101.45	3.773%	$105.2777	$105.28	$105.30	$105.30
7 purchase totals =	$827.56		$903.0163	$903.03	$903.00	$903.10