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	$100.46	4.774%	$105.256	$105.26	$105.25	$105.30
Purchase #2	$48.41	8.393%	$52.4731	$52.47	$52.45	$52.50
Purchase #3	$46.73	11.451%	$52.0811	$52.08	$52.10	$52.10
Purchase #4	$86.53	12.548%	$97.3878	$97.39	$97.40	$97.40
Purchase #5	$55.52	7.231%	$59.5347	$59.53	$59.55	$59.50
Purchase #6	$132.97	3.220%	$137.2516	$137.25	$137.25	$137.30
Purchase #7	$70.75	10.754%	$78.3585	$78.36	$78.35	$78.40
7 purchase totals =	$541.37		$582.3428	$582.34	$582.35	$582.50