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	$133.50	12.680%	$150.4278	$150.43	$150.45	$150.40
Purchase #2	$90.79	11.719%	$101.4297	$101.43	$101.45	$101.40
Purchase #3	$146.36	13.483%	$166.0937	$166.09	$166.10	$166.10
Purchase #4	$75.40	5.421%	$79.4874	$79.49	$79.50	$79.50
Purchase #5	$74.29	12.429%	$83.5235	$83.52	$83.50	$83.50
Purchase #6	$224.99	13.817%	$256.0769	$256.08	$256.10	$256.10
Purchase #7	$39.79	4.342%	$41.5177	$41.52	$41.50	$41.50
7 purchase totals =	$785.12		$878.5567	$878.56	$878.60	$878.50