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	$34.75	9.840%	$38.1694	$38.17	$38.15	$38.20
Purchase #2	$95.38	8.416%	$103.4072	$103.41	$103.40	$103.40
Purchase #3	$63.27	4.318%	$66.002	$66.00	$66.00	$66.00
Purchase #4	$41.88	4.614%	$43.8123	$43.81	$43.80	$43.80
Purchase #5	$100.56	4.855%	$105.4422	$105.44	$105.45	$105.40
Purchase #6	$9.69	10.857%	$10.742	$10.74	$10.75	$10.70
Purchase #7	$165.74	10.526%	$183.1858	$183.19	$183.20	$183.20
7 purchase totals =	$511.27		$550.7609	$550.76	$550.75	$550.70