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	$118.92	10.260%	$131.1212	$131.12	$131.10	$131.10
Purchase #2	$78.63	8.148%	$85.0368	$85.04	$85.05	$85.00
Purchase #3	$99.47	11.636%	$111.0443	$111.04	$111.05	$111.00
Purchase #4	$95.66	8.383%	$103.6792	$103.68	$103.70	$103.70
Purchase #5	$26.93	4.677%	$28.1895	$28.19	$28.20	$28.20
Purchase #6	$91.92	13.724%	$104.5351	$104.54	$104.55	$104.50
Purchase #7	$49.25	4.829%	$51.6283	$51.63	$51.65	$51.60
7 purchase totals =	$560.78		$615.2344	$615.24	$615.30	$615.10