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	$159.75	12.129%	$179.1261	$179.13	$179.15	$179.10
Purchase #2	$100.54	10.668%	$111.2656	$111.27	$111.25	$111.30
Purchase #3	$201.34	6.373%	$214.1714	$214.17	$214.15	$214.20
Purchase #4	$108.57	6.412%	$115.5315	$115.53	$115.55	$115.50
Purchase #5	$37.48	8.189%	$40.5492	$40.55	$40.55	$40.50
Purchase #6	$118.52	13.221%	$134.1895	$134.19	$134.20	$134.20
Purchase #7	$40.81	11.869%	$45.6537	$45.65	$45.65	$45.70
7 purchase totals =	$767.01		$840.4870	$840.49	$840.50	$840.50