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	$57.28	13.704%	$65.1297	$65.13	$65.15	$65.10
Purchase #2	$90.57	10.567%	$100.1405	$100.14	$100.15	$100.10
Purchase #3	$28.58	4.353%	$29.8241	$29.82	$29.80	$29.80
Purchase #4	$144.35	5.629%	$152.4755	$152.48	$152.50	$152.50
Purchase #5	$25.85	4.544%	$27.0246	$27.02	$27.00	$27.00
Purchase #6	$79.75	13.453%	$90.4788	$90.48	$90.50	$90.50
Purchase #7	$79.55	3.849%	$82.6119	$82.61	$82.60	$82.60
7 purchase totals =	$505.93		$547.6851	$547.68	$547.70	$547.60