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	$122.54	12.326%	$137.6443	$137.64	$137.65	$137.60
Purchase #2	$89.83	8.303%	$97.2886	$97.29	$97.30	$97.30
Purchase #3	$21.52	12.744%	$24.2625	$24.26	$24.25	$24.30
Purchase #4	$158.85	9.354%	$173.7088	$173.71	$173.70	$173.70
Purchase #5	$33.74	12.459%	$37.9437	$37.94	$37.95	$37.90
Purchase #6	$72.69	13.612%	$82.5846	$82.58	$82.60	$82.60
Purchase #7	$104.86	4.246%	$109.3124	$109.31	$109.30	$109.30
7 purchase totals =	$604.03		$662.7449	$662.73	$662.75	$662.70