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	$80.77	9.668%	$88.5788	$88.58	$88.60	$88.60
Purchase #2	$161.56	7.231%	$173.2424	$173.24	$173.25	$173.20
Purchase #3	$204.37	5.193%	$214.9829	$214.98	$215.00	$215.00
Purchase #4	$26.39	3.442%	$27.2983	$27.30	$27.30	$27.30
Purchase #5	$166.48	3.868%	$172.9194	$172.92	$172.90	$172.90
Purchase #6	$160.40	7.275%	$172.0691	$172.07	$172.05	$172.10
Purchase #7	$140.35	13.240%	$158.9323	$158.93	$158.95	$158.90
7 purchase totals =	$940.32		$1,008.0232	$1,008.02	$1,008.05	$1,008.00