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	$51.61	11.581%	$57.587	$57.59	$57.60	$57.60
Purchase #2	$57.30	5.262%	$60.3151	$60.32	$60.30	$60.30
Purchase #3	$239.96	13.454%	$272.2442	$272.24	$272.25	$272.20
Purchase #4	$224.50	6.301%	$238.6457	$238.65	$238.65	$238.60
Purchase #5	$59.69	11.623%	$66.6278	$66.63	$66.65	$66.60
Purchase #6	$178.35	9.560%	$195.4003	$195.40	$195.40	$195.40
Purchase #7	$119.91	7.526%	$128.9344	$128.93	$128.95	$128.90
7 purchase totals =	$931.32		$1,019.7545	$1,019.76	$1,019.80	$1,019.60