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	$56.55	5.737%	$59.7943	$59.79	$59.80	$59.80
Purchase #2	$185.58	10.650%	$205.3443	$205.34	$205.35	$205.30
Purchase #3	$191.78	10.290%	$211.5142	$211.51	$211.50	$211.50
Purchase #4	$103.28	8.280%	$111.8316	$111.83	$111.85	$111.80
Purchase #5	$71.68	13.593%	$81.4235	$81.42	$81.40	$81.40
Purchase #6	$169.40	4.270%	$176.6334	$176.63	$176.65	$176.60
Purchase #7	$154.75	4.749%	$162.0991	$162.10	$162.10	$162.10
7 purchase totals =	$933.02		$1,008.6404	$1,008.62	$1,008.65	$1,008.50