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	$81.26	9.786%	$89.2121	$89.21	$89.20	$89.20
Purchase #2	$212.33	12.667%	$239.2258	$239.23	$239.25	$239.20
Purchase #3	$12.51	10.762%	$13.8563	$13.86	$13.85	$13.90
Purchase #4	$57.76	5.347%	$60.8484	$60.85	$60.85	$60.80
Purchase #5	$133.39	7.741%	$143.7157	$143.72	$143.70	$143.70
Purchase #6	$186.30	4.408%	$194.5121	$194.51	$194.50	$194.50
Purchase #7	$92.63	13.599%	$105.2268	$105.23	$105.25	$105.20
7 purchase totals =	$776.18		$846.5972	$846.61	$846.60	$846.50