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	$73.30	12.553%	$82.5013	$82.50	$82.50	$82.50
Purchase #2	$132.58	3.806%	$137.626	$137.63	$137.65	$137.60
Purchase #3	$233.42	9.843%	$256.3955	$256.40	$256.40	$256.40
Purchase #4	$38.30	13.685%	$43.5414	$43.54	$43.55	$43.50
Purchase #5	$19.33	6.781%	$20.6408	$20.64	$20.65	$20.60
Purchase #6	$136.97	10.103%	$150.8081	$150.81	$150.80	$150.80
Purchase #7	$70.76	4.762%	$74.1296	$74.13	$74.15	$74.10
7 purchase totals =	$704.66		$765.6427	$765.65	$765.70	$765.50