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	$9.41	10.477%	$10.3959	$10.40	$10.40	$10.40
Purchase #2	$29.42	6.795%	$31.4191	$31.42	$31.40	$31.40
Purchase #3	$55.70	3.343%	$57.5621	$57.56	$57.55	$57.60
Purchase #4	$131.77	9.431%	$144.1972	$144.20	$144.20	$144.20
Purchase #5	$111.92	13.399%	$126.9162	$126.92	$126.90	$126.90
Purchase #6	$119.99	6.223%	$127.457	$127.46	$127.45	$127.50
Purchase #7	$156.46	10.834%	$173.4109	$173.41	$173.40	$173.40
7 purchase totals =	$614.67		$671.3584	$671.37	$671.30	$671.40