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	$79.93	13.193%	$90.4752	$90.48	$90.50	$90.50
Purchase #2	$103.97	9.379%	$113.7213	$113.72	$113.70	$113.70
Purchase #3	$192.38	13.512%	$218.3744	$218.37	$218.35	$218.40
Purchase #4	$227.82	11.634%	$254.3246	$254.32	$254.30	$254.30
Purchase #5	$141.41	6.749%	$150.9538	$150.95	$150.95	$151.00
Purchase #6	$152.86	5.110%	$160.6711	$160.67	$160.65	$160.70
Purchase #7	$41.77	3.320%	$43.1568	$43.16	$43.15	$43.20
7 purchase totals =	$940.14		$1,031.6772	$1,031.67	$1,031.60	$1,031.80