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	$89.78	10.702%	$99.3883	$99.39	$99.40	$99.40
Purchase #2	$140.25	8.643%	$152.3718	$152.37	$152.35	$152.40
Purchase #3	$196.80	13.192%	$222.7619	$222.76	$222.75	$222.80
Purchase #4	$14.90	4.806%	$15.6161	$15.62	$15.60	$15.60
Purchase #5	$228.78	11.600%	$255.3185	$255.32	$255.30	$255.30
Purchase #6	$68.41	9.292%	$74.7667	$74.77	$74.75	$74.80
Purchase #7	$5.80	6.274%	$6.1639	$6.16	$6.15	$6.20
7 purchase totals =	$744.72		$826.3872	$826.39	$826.30	$826.50