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	$145.96	5.108%	$153.4156	$153.42	$153.40	$153.40
Purchase #2	$61.26	4.712%	$64.1466	$64.15	$64.15	$64.10
Purchase #3	$162.34	11.583%	$181.1438	$181.14	$181.15	$181.10
Purchase #4	$158.89	8.455%	$172.3241	$172.32	$172.30	$172.30
Purchase #5	$5.47	11.181%	$6.0816	$6.08	$6.10	$6.10
Purchase #6	$6.37	3.597%	$6.5991	$6.60	$6.60	$6.60
Purchase #7	$21.52	4.311%	$22.4477	$22.45	$22.45	$22.40
7 purchase totals =	$561.81		$606.1585	$606.16	$606.15	$606.00