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	$39.31	7.777%	$42.3671	$42.37	$42.35	$42.40
Purchase #2	$111.87	4.799%	$117.2386	$117.24	$117.25	$117.20
Purchase #3	$226.88	13.842%	$258.2847	$258.28	$258.30	$258.30
Purchase #4	$79.89	8.211%	$86.4498	$86.45	$86.45	$86.40
Purchase #5	$176.95	10.147%	$194.9051	$194.91	$194.90	$194.90
Purchase #6	$136.37	7.247%	$146.2527	$146.25	$146.25	$146.30
Purchase #7	$226.31	3.127%	$233.3867	$233.39	$233.40	$233.40
7 purchase totals =	$997.58		$1,078.8847	$1,078.89	$1,078.90	$1,078.90