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	$184.69	8.104%	$199.6573	$199.66	$199.65	$199.70
Purchase #2	$54.46	3.272%	$56.2419	$56.24	$56.25	$56.20
Purchase #3	$132.51	12.302%	$148.8114	$148.81	$148.80	$148.80
Purchase #4	$128.56	12.177%	$144.2148	$144.21	$144.20	$144.20
Purchase #5	$104.65	4.450%	$109.3069	$109.31	$109.30	$109.30
Purchase #6	$48.66	3.605%	$50.4142	$50.41	$50.40	$50.40
Purchase #7	$105.59	5.336%	$111.2243	$111.22	$111.20	$111.20
7 purchase totals =	$759.12		$819.8708	$819.86	$819.80	$819.80