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	$19.38	11.434%	$21.5959	$21.60	$21.60	$21.60
Purchase #2	$183.71	13.748%	$208.9665	$208.97	$208.95	$209.00
Purchase #3	$222.39	7.126%	$238.2375	$238.24	$238.25	$238.20
Purchase #4	$53.69	11.173%	$59.6888	$59.69	$59.70	$59.70
Purchase #5	$100.39	8.680%	$109.1039	$109.10	$109.10	$109.10
Purchase #6	$188.61	5.106%	$198.2404	$198.24	$198.25	$198.20
Purchase #7	$215.93	13.124%	$244.2687	$244.27	$244.25	$244.30
7 purchase totals =	$984.10		$1,080.1017	$1,080.11	$1,080.10	$1,080.10