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	$106.43	10.136%	$117.2177	$117.22	$117.20	$117.20
Purchase #2	$147.79	8.263%	$160.0019	$160.00	$160.00	$160.00
Purchase #3	$48.52	12.358%	$54.5161	$54.52	$54.50	$54.50
Purchase #4	$127.59	3.106%	$131.5529	$131.55	$131.55	$131.60
Purchase #5	$94.94	4.525%	$99.236	$99.24	$99.25	$99.20
Purchase #6	$194.47	5.688%	$205.5315	$205.53	$205.55	$205.50
Purchase #7	$192.91	9.684%	$211.5914	$211.59	$211.60	$211.60
7 purchase totals =	$912.65		$979.6475	$979.65	$979.65	$979.60