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	$70.40	11.829%	$78.7276	$78.73	$78.75	$78.70
Purchase #2	$94.47	5.247%	$99.4268	$99.43	$99.45	$99.40
Purchase #3	$237.50	7.565%	$255.4669	$255.47	$255.45	$255.50
Purchase #4	$17.60	5.261%	$18.5259	$18.53	$18.55	$18.50
Purchase #5	$21.29	9.868%	$23.3909	$23.39	$23.40	$23.40
Purchase #6	$105.94	10.398%	$116.9556	$116.96	$116.95	$117.00
Purchase #7	$73.71	7.839%	$79.4881	$79.49	$79.50	$79.50
7 purchase totals =	$620.91		$671.9818	$672.00	$672.05	$672.00