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	$112.68	5.172%	$118.5078	$118.51	$118.50	$118.50
Purchase #2	$40.96	6.188%	$43.4946	$43.49	$43.50	$43.50
Purchase #3	$156.70	9.208%	$171.1289	$171.13	$171.15	$171.10
Purchase #4	$55.51	13.634%	$63.0782	$63.08	$63.10	$63.10
Purchase #5	$118.32	10.527%	$130.7755	$130.78	$130.80	$130.80
Purchase #6	$36.69	9.791%	$40.2823	$40.28	$40.30	$40.30
Purchase #7	$247.42	11.671%	$276.2964	$276.30	$276.30	$276.30
7 purchase totals =	$768.28		$843.5637	$843.57	$843.65	$843.60