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	$250.27	11.635%	$279.3889	$279.39	$279.40	$279.40
Purchase #2	$24.68	11.561%	$27.5333	$27.53	$27.55	$27.50
Purchase #3	$78.62	10.523%	$86.8932	$86.89	$86.90	$86.90
Purchase #4	$158.80	9.786%	$174.3402	$174.34	$174.35	$174.30
Purchase #5	$98.80	7.114%	$105.8286	$105.83	$105.85	$105.80
Purchase #6	$60.53	10.810%	$67.0733	$67.07	$67.05	$67.10
Purchase #7	$143.38	7.203%	$153.7077	$153.71	$153.70	$153.70
7 purchase totals =	$815.08		$894.7652	$894.76	$894.80	$894.70