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	$39.37	6.693%	$42.005	$42.01	$42.00	$42.00
Purchase #2	$208.53	10.330%	$230.0711	$230.07	$230.05	$230.10
Purchase #3	$200.56	4.429%	$209.4428	$209.44	$209.45	$209.40
Purchase #4	$103.78	12.499%	$116.7515	$116.75	$116.75	$116.80
Purchase #5	$61.40	4.531%	$64.182	$64.18	$64.20	$64.20
Purchase #6	$178.96	5.326%	$188.4914	$188.49	$188.50	$188.50
Purchase #7	$140.40	7.631%	$151.1139	$151.11	$151.10	$151.10
7 purchase totals =	$933.00		$1,002.0577	$1,002.05	$1,002.05	$1,002.10