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	$236.93	4.467%	$247.5137	$247.51	$247.50	$247.50
Purchase #2	$169.80	11.848%	$189.9179	$189.92	$189.90	$189.90
Purchase #3	$47.80	9.695%	$52.4342	$52.43	$52.45	$52.40
Purchase #4	$83.38	12.781%	$94.0368	$94.04	$94.05	$94.00
Purchase #5	$144.71	7.514%	$155.5835	$155.58	$155.60	$155.60
Purchase #6	$33.95	11.358%	$37.806	$37.81	$37.80	$37.80
Purchase #7	$145.81	8.871%	$158.7448	$158.74	$158.75	$158.70
7 purchase totals =	$862.38		$936.0369	$936.03	$936.05	$935.90