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	$130.30	10.704%	$144.2473	$144.25	$144.25	$144.20
Purchase #2	$46.88	6.466%	$49.9113	$49.91	$49.90	$49.90
Purchase #3	$37.42	8.460%	$40.5857	$40.59	$40.60	$40.60
Purchase #4	$177.45	3.292%	$183.2917	$183.29	$183.30	$183.30
Purchase #5	$27.42	6.725%	$29.264	$29.26	$29.25	$29.30
Purchase #6	$96.81	8.621%	$105.156	$105.16	$105.15	$105.20
Purchase #7	$151.54	7.178%	$162.4175	$162.42	$162.40	$162.40
7 purchase totals =	$667.82		$714.8735	$714.88	$714.85	$714.90