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	$100.78	3.344%	$104.1501	$104.15	$104.15	$104.20
Purchase #2	$34.30	7.450%	$36.8554	$36.86	$36.85	$36.90
Purchase #3	$110.97	6.615%	$118.3107	$118.31	$118.30	$118.30
Purchase #4	$10.90	8.502%	$11.8267	$11.83	$11.85	$11.80
Purchase #5	$10.80	8.382%	$11.7053	$11.71	$11.70	$11.70
Purchase #6	$73.78	11.555%	$82.3053	$82.31	$82.30	$82.30
Purchase #7	$57.77	13.326%	$65.4684	$65.47	$65.45	$65.50
7 purchase totals =	$399.30		$430.6219	$430.64	$430.60	$430.70