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	$135.43	5.794%	$143.2768	$143.28	$143.30	$143.30
Purchase #2	$249.39	8.856%	$271.476	$271.48	$271.50	$271.50
Purchase #3	$162.52	4.841%	$170.3876	$170.39	$170.40	$170.40
Purchase #4	$121.74	4.722%	$127.4886	$127.49	$127.50	$127.50
Purchase #5	$37.60	11.545%	$41.9409	$41.94	$41.95	$41.90
Purchase #6	$236.86	13.384%	$268.5613	$268.56	$268.55	$268.60
Purchase #7	$154.34	12.105%	$173.0229	$173.02	$173.00	$173.00
7 purchase totals =	$1,097.88		$1,196.1541	$1,196.16	$1,196.20	$1,196.20