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	$29.83	8.235%	$32.2865	$32.29	$32.30	$32.30
Purchase #2	$5.71	9.308%	$6.2415	$6.24	$6.25	$6.20
Purchase #3	$76.43	9.108%	$83.3912	$83.39	$83.40	$83.40
Purchase #4	$119.72	6.602%	$127.6239	$127.62	$127.60	$127.60
Purchase #5	$123.62	12.479%	$139.0465	$139.05	$139.05	$139.00
Purchase #6	$138.92	9.858%	$152.6147	$152.61	$152.60	$152.60
Purchase #7	$89.27	9.730%	$97.956	$97.96	$97.95	$98.00
7 purchase totals =	$583.50		$639.1603	$639.16	$639.15	$639.10