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	$8.39	8.455%	$9.0994	$9.10	$9.10	$9.10
Purchase #2	$113.90	12.255%	$127.8584	$127.86	$127.85	$127.90
Purchase #3	$206.94	4.809%	$216.8917	$216.89	$216.90	$216.90
Purchase #4	$15.85	12.599%	$17.8469	$17.85	$17.85	$17.80
Purchase #5	$10.70	13.675%	$12.1632	$12.16	$12.15	$12.20
Purchase #6	$42.64	6.544%	$45.4304	$45.43	$45.45	$45.40
Purchase #7	$63.72	12.474%	$71.6684	$71.67	$71.65	$71.70
7 purchase totals =	$462.14		$500.9584	$500.96	$500.95	$501.00