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	$44.28	6.599%	$47.202	$47.20	$47.20	$47.20
Purchase #2	$103.72	12.870%	$117.0688	$117.07	$117.05	$117.10
Purchase #3	$66.31	4.127%	$69.0466	$69.05	$69.05	$69.00
Purchase #4	$152.25	4.196%	$158.6384	$158.64	$158.65	$158.60
Purchase #5	$19.97	4.490%	$20.8667	$20.87	$20.85	$20.90
Purchase #6	$105.37	5.864%	$111.5489	$111.55	$111.55	$111.50
Purchase #7	$118.49	4.296%	$123.5803	$123.58	$123.60	$123.60
7 purchase totals =	$610.39		$647.9517	$647.96	$647.95	$647.90