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	$249.31	10.663%	$275.8939	$275.89	$275.90	$275.90
Purchase #2	$94.57	10.655%	$104.6464	$104.65	$104.65	$104.60
Purchase #3	$250.99	13.433%	$284.7055	$284.71	$284.70	$284.70
Purchase #4	$81.47	4.815%	$85.3928	$85.39	$85.40	$85.40
Purchase #5	$158.75	4.136%	$165.3159	$165.32	$165.30	$165.30
Purchase #6	$109.58	11.710%	$122.4118	$122.41	$122.40	$122.40
Purchase #7	$127.80	3.852%	$132.7229	$132.72	$132.70	$132.70
7 purchase totals =	$1,072.47		$1,171.0892	$1,171.09	$1,171.05	$1,171.00