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	$51.57	12.274%	$57.8997	$57.90	$57.90	$57.90
Purchase #2	$139.62	10.615%	$154.4407	$154.44	$154.45	$154.40
Purchase #3	$40.25	5.696%	$42.5426	$42.54	$42.55	$42.50
Purchase #4	$58.57	13.458%	$66.4524	$66.45	$66.45	$66.50
Purchase #5	$89.73	10.719%	$99.3482	$99.35	$99.35	$99.30
Purchase #6	$82.84	4.861%	$86.8669	$86.87	$86.85	$86.90
Purchase #7	$241.60	4.332%	$252.0661	$252.07	$252.05	$252.10
7 purchase totals =	$704.18		$759.6166	$759.62	$759.60	$759.60