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	$90.39	10.340%	$99.7363	$99.74	$99.75	$99.70
Purchase #2	$165.93	7.772%	$178.8261	$178.83	$178.85	$178.80
Purchase #3	$205.99	4.788%	$215.8528	$215.85	$215.85	$215.90
Purchase #4	$70.66	9.841%	$77.6137	$77.61	$77.60	$77.60
Purchase #5	$152.82	12.327%	$171.6581	$171.66	$171.65	$171.70
Purchase #6	$167.26	5.331%	$176.1766	$176.18	$176.20	$176.20
Purchase #7	$116.30	13.187%	$131.6365	$131.64	$131.65	$131.60
7 purchase totals =	$969.35		$1,051.5001	$1,051.51	$1,051.55	$1,051.50