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	$205.80	5.832%	$217.8023	$217.80	$217.80	$217.80
Purchase #2	$123.40	3.311%	$127.4858	$127.49	$127.50	$127.50
Purchase #3	$188.41	10.456%	$208.1101	$208.11	$208.10	$208.10
Purchase #4	$109.94	4.424%	$114.8037	$114.80	$114.80	$114.80
Purchase #5	$127.29	13.724%	$144.7593	$144.76	$144.75	$144.80
Purchase #6	$16.97	5.607%	$17.9215	$17.92	$17.90	$17.90
Purchase #7	$55.52	10.283%	$61.2291	$61.23	$61.25	$61.20
7 purchase totals =	$827.33		$892.1118	$892.11	$892.10	$892.10