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	$234.42	6.768%	$250.2855	$250.29	$250.30	$250.30
Purchase #2	$250.31	7.476%	$269.0232	$269.02	$269.00	$269.00
Purchase #3	$74.69	10.570%	$82.5847	$82.58	$82.60	$82.60
Purchase #4	$49.48	11.728%	$55.283	$55.28	$55.30	$55.30
Purchase #5	$205.30	10.654%	$227.1727	$227.17	$227.15	$227.20
Purchase #6	$214.34	12.722%	$241.6083	$241.61	$241.60	$241.60
Purchase #7	$145.42	5.788%	$153.8369	$153.84	$153.85	$153.80
7 purchase totals =	$1,173.96		$1,279.7943	$1,279.79	$1,279.80	$1,279.80