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	$11.47	7.559%	$12.337	$12.34	$12.35	$12.30
Purchase #2	$18.31	11.839%	$20.4777	$20.48	$20.50	$20.50
Purchase #3	$233.76	8.219%	$252.9727	$252.97	$252.95	$253.00
Purchase #4	$43.68	9.726%	$47.9283	$47.93	$47.95	$47.90
Purchase #5	$84.43	5.781%	$89.3109	$89.31	$89.30	$89.30
Purchase #6	$41.89	8.739%	$45.5508	$45.55	$45.55	$45.60
Purchase #7	$46.63	8.436%	$50.5637	$50.56	$50.55	$50.60
7 purchase totals =	$480.17		$519.1411	$519.14	$519.15	$519.20