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	$19.38	5.451%	$20.4364	$20.44	$20.45	$20.40
Purchase #2	$81.64	5.496%	$86.1269	$86.13	$86.15	$86.10
Purchase #3	$118.76	13.235%	$134.4779	$134.48	$134.50	$134.50
Purchase #4	$170.98	13.431%	$193.9443	$193.94	$193.95	$193.90
Purchase #5	$40.35	4.581%	$42.1984	$42.20	$42.20	$42.20
Purchase #6	$116.85	5.492%	$123.2674	$123.27	$123.25	$123.30
Purchase #7	$47.93	13.542%	$54.4207	$54.42	$54.40	$54.40
7 purchase totals =	$595.89		$654.8720	$654.88	$654.90	$654.80