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	$9.57	8.722%	$10.4047	$10.40	$10.40	$10.40
Purchase #2	$160.68	7.377%	$172.5334	$172.53	$172.55	$172.50
Purchase #3	$222.58	7.307%	$238.8439	$238.84	$238.85	$238.80
Purchase #4	$124.94	13.326%	$141.5895	$141.59	$141.60	$141.60
Purchase #5	$229.34	12.298%	$257.5442	$257.54	$257.55	$257.50
Purchase #6	$90.87	13.714%	$103.3319	$103.33	$103.35	$103.30
Purchase #7	$250.91	3.398%	$259.4359	$259.44	$259.45	$259.40
7 purchase totals =	$1,088.89		$1,183.6835	$1,183.67	$1,183.75	$1,183.50