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	$100.56	11.772%	$112.3979	$112.40	$112.40	$112.40
Purchase #2	$228.88	4.156%	$238.3923	$238.39	$238.40	$238.40
Purchase #3	$132.47	5.174%	$139.324	$139.32	$139.30	$139.30
Purchase #4	$47.96	6.256%	$50.9604	$50.96	$50.95	$51.00
Purchase #5	$242.40	12.426%	$272.5206	$272.52	$272.50	$272.50
Purchase #6	$157.61	6.301%	$167.541	$167.54	$167.55	$167.50
Purchase #7	$244.72	12.670%	$275.726	$275.73	$275.75	$275.70
7 purchase totals =	$1,154.60		$1,256.8622	$1,256.86	$1,256.85	$1,256.80