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	$57.99	13.413%	$65.7682	$65.77	$65.75	$65.80
Purchase #2	$141.63	7.522%	$152.2834	$152.28	$152.30	$152.30
Purchase #3	$19.76	3.318%	$20.4156	$20.42	$20.40	$20.40
Purchase #4	$247.27	11.171%	$274.8925	$274.89	$274.90	$274.90
Purchase #5	$145.38	11.340%	$161.8661	$161.87	$161.85	$161.90
Purchase #6	$94.83	9.530%	$103.8673	$103.87	$103.85	$103.90
Purchase #7	$15.49	12.186%	$17.3776	$17.38	$17.40	$17.40
7 purchase totals =	$722.35		$796.4707	$796.48	$796.45	$796.60