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	$241.31	11.480%	$269.0124	$269.01	$269.00	$269.00
Purchase #2	$60.74	12.663%	$68.4315	$68.43	$68.45	$68.40
Purchase #3	$46.61	10.131%	$51.3321	$51.33	$51.35	$51.30
Purchase #4	$46.36	6.869%	$49.5445	$49.54	$49.55	$49.50
Purchase #5	$99.87	5.280%	$105.1431	$105.14	$105.15	$105.10
Purchase #6	$18.41	3.852%	$19.1192	$19.12	$19.10	$19.10
Purchase #7	$116.27	9.651%	$127.4912	$127.49	$127.50	$127.50
7 purchase totals =	$629.57		$690.0740	$690.06	$690.10	$689.90