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	$40.31	9.488%	$44.1346	$44.13	$44.15	$44.10
Purchase #2	$65.70	3.196%	$67.7998	$67.80	$67.80	$67.80
Purchase #3	$242.40	6.700%	$258.6408	$258.64	$258.65	$258.60
Purchase #4	$154.65	7.733%	$166.6091	$166.61	$166.60	$166.60
Purchase #5	$177.93	11.566%	$198.5094	$198.51	$198.50	$198.50
Purchase #6	$63.54	11.384%	$70.7734	$70.77	$70.75	$70.80
Purchase #7	$47.98	13.200%	$54.3134	$54.31	$54.30	$54.30
7 purchase totals =	$792.51		$860.7805	$860.77	$860.75	$860.70