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	$50.45	13.208%	$57.1134	$57.11	$57.10	$57.10
Purchase #2	$159.70	6.510%	$170.0965	$170.10	$170.10	$170.10
Purchase #3	$142.38	12.708%	$160.4737	$160.47	$160.45	$160.50
Purchase #4	$174.78	11.571%	$195.0038	$195.00	$195.00	$195.00
Purchase #5	$124.98	5.412%	$131.7439	$131.74	$131.75	$131.70
Purchase #6	$13.85	11.207%	$15.4022	$15.40	$15.40	$15.40
Purchase #7	$92.72	13.613%	$105.342	$105.34	$105.35	$105.30
7 purchase totals =	$758.86		$835.1755	$835.16	$835.15	$835.10