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	$146.41	13.513%	$166.1944	$166.19	$166.20	$166.20
Purchase #2	$33.46	5.115%	$35.1715	$35.17	$35.15	$35.20
Purchase #3	$71.32	3.358%	$73.7149	$73.71	$73.70	$73.70
Purchase #4	$129.76	8.648%	$140.9816	$140.98	$141.00	$141.00
Purchase #5	$74.56	5.730%	$78.8323	$78.83	$78.85	$78.80
Purchase #6	$25.96	12.235%	$29.1362	$29.14	$29.15	$29.10
Purchase #7	$121.85	4.274%	$127.0579	$127.06	$127.05	$127.10
7 purchase totals =	$603.32		$651.0888	$651.08	$651.10	$651.10