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	$248.43	12.124%	$278.5497	$278.55	$278.55	$278.50
Purchase #2	$71.44	9.856%	$78.4811	$78.48	$78.50	$78.50
Purchase #3	$120.35	9.535%	$131.8254	$131.83	$131.85	$131.80
Purchase #4	$183.33	13.250%	$207.6212	$207.62	$207.60	$207.60
Purchase #5	$194.93	12.439%	$219.1773	$219.18	$219.20	$219.20
Purchase #6	$45.83	12.660%	$51.6321	$51.63	$51.65	$51.60
Purchase #7	$127.71	13.739%	$145.2561	$145.26	$145.25	$145.30
7 purchase totals =	$992.02		$1,112.5429	$1,112.55	$1,112.60	$1,112.50