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	$228.89	8.812%	$249.0598	$249.06	$249.05	$249.10
Purchase #2	$153.86	3.499%	$159.2436	$159.24	$159.25	$159.20
Purchase #3	$74.49	11.103%	$82.7606	$82.76	$82.75	$82.80
Purchase #4	$147.53	8.394%	$159.9137	$159.91	$159.90	$159.90
Purchase #5	$93.29	10.865%	$103.426	$103.43	$103.45	$103.40
Purchase #6	$249.60	12.447%	$280.6677	$280.67	$280.65	$280.70
Purchase #7	$23.30	13.287%	$26.3959	$26.40	$26.40	$26.40
7 purchase totals =	$970.96		$1,061.4673	$1,061.47	$1,061.45	$1,061.50