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	$6.80	6.114%	$7.2158	$7.22	$7.20	$7.20
Purchase #2	$240.78	9.117%	$262.7319	$262.73	$262.75	$262.70
Purchase #3	$164.54	9.782%	$180.6353	$180.64	$180.65	$180.60
Purchase #4	$233.66	4.476%	$244.1186	$244.12	$244.10	$244.10
Purchase #5	$172.71	5.153%	$181.6097	$181.61	$181.60	$181.60
Purchase #6	$73.71	12.850%	$83.1817	$83.18	$83.20	$83.20
Purchase #7	$112.76	13.144%	$127.5812	$127.58	$127.60	$127.60
7 purchase totals =	$1,004.96		$1,087.0742	$1,087.08	$1,087.10	$1,087.00