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	$21.87	6.554%	$23.3034	$23.30	$23.30	$23.30
Purchase #2	$41.32	9.581%	$45.2789	$45.28	$45.30	$45.30
Purchase #3	$43.69	7.699%	$47.0537	$47.05	$47.05	$47.10
Purchase #4	$38.69	8.242%	$41.8788	$41.88	$41.90	$41.90
Purchase #5	$42.72	6.547%	$45.5169	$45.52	$45.50	$45.50
Purchase #6	$132.91	8.682%	$144.4492	$144.45	$144.45	$144.40
Purchase #7	$73.91	11.563%	$82.4562	$82.46	$82.45	$82.50
7 purchase totals =	$395.11		$429.9371	$429.94	$429.95	$430.00