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	$71.81	4.124%	$74.7714	$74.77	$74.75	$74.80
Purchase #2	$42.87	12.554%	$48.2519	$48.25	$48.25	$48.30
Purchase #3	$179.78	6.636%	$191.7102	$191.71	$191.70	$191.70
Purchase #4	$99.26	3.826%	$103.0577	$103.06	$103.05	$103.10
Purchase #5	$151.39	8.669%	$164.514	$164.51	$164.50	$164.50
Purchase #6	$37.53	13.518%	$42.6033	$42.60	$42.60	$42.60
Purchase #7	$49.70	10.794%	$55.0646	$55.06	$55.05	$55.10
7 purchase totals =	$632.34		$679.9731	$679.96	$679.90	$680.10