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	$11.88	11.312%	$13.2239	$13.22	$13.20	$13.20
Purchase #2	$103.35	4.581%	$108.0845	$108.08	$108.10	$108.10
Purchase #3	$191.84	3.351%	$198.2686	$198.27	$198.25	$198.30
Purchase #4	$49.32	7.581%	$53.0589	$53.06	$53.05	$53.10
Purchase #5	$38.66	9.820%	$42.4564	$42.46	$42.45	$42.50
Purchase #6	$34.26	8.385%	$37.1327	$37.13	$37.15	$37.10
Purchase #7	$44.54	9.834%	$48.9201	$48.92	$48.90	$48.90
7 purchase totals =	$473.85		$501.1451	$501.14	$501.10	$501.20