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	$38.72	9.758%	$42.4983	$42.50	$42.50	$42.50
Purchase #2	$233.53	3.615%	$241.9721	$241.97	$241.95	$242.00
Purchase #3	$18.81	7.815%	$20.28	$20.28	$20.30	$20.30
Purchase #4	$238.74	7.847%	$257.4739	$257.47	$257.45	$257.50
Purchase #5	$212.85	11.679%	$237.7088	$237.71	$237.70	$237.70
Purchase #6	$82.29	9.132%	$89.8047	$89.80	$89.80	$89.80
Purchase #7	$30.54	6.691%	$32.5834	$32.58	$32.60	$32.60
7 purchase totals =	$855.48		$922.3212	$922.31	$922.30	$922.40