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	$56.89	6.343%	$60.4985	$60.50	$60.50	$60.50
Purchase #2	$185.66	11.467%	$206.9496	$206.95	$206.95	$206.90
Purchase #3	$36.64	5.320%	$38.5892	$38.59	$38.60	$38.60
Purchase #4	$133.78	4.224%	$139.4309	$139.43	$139.45	$139.40
Purchase #5	$182.60	7.140%	$195.6376	$195.64	$195.65	$195.60
Purchase #6	$59.58	9.534%	$65.2604	$65.26	$65.25	$65.30
Purchase #7	$50.66	13.506%	$57.5021	$57.50	$57.50	$57.50
7 purchase totals =	$705.81		$763.8683	$763.87	$763.90	$763.80