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	$157.73	8.685%	$171.4289	$171.43	$171.45	$171.40
Purchase #2	$182.77	13.842%	$208.069	$208.07	$208.05	$208.10
Purchase #3	$41.27	10.281%	$45.513	$45.51	$45.50	$45.50
Purchase #4	$54.86	4.157%	$57.1405	$57.14	$57.15	$57.10
Purchase #5	$234.46	5.566%	$247.51	$247.51	$247.50	$247.50
Purchase #6	$102.65	9.859%	$112.7703	$112.77	$112.75	$112.80
Purchase #7	$144.40	3.526%	$149.4915	$149.49	$149.50	$149.50
7 purchase totals =	$918.14		$991.9232	$991.92	$991.90	$991.90