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	$126.31	10.366%	$139.4033	$139.40	$139.40	$139.40
Purchase #2	$238.52	6.744%	$254.6058	$254.61	$254.60	$254.60
Purchase #3	$53.86	7.563%	$57.9334	$57.93	$57.95	$57.90
Purchase #4	$199.73	7.575%	$214.8595	$214.86	$214.85	$214.90
Purchase #5	$239.77	12.550%	$269.8611	$269.86	$269.85	$269.90
Purchase #6	$134.95	5.497%	$142.3682	$142.37	$142.35	$142.40
Purchase #7	$148.38	9.757%	$162.8574	$162.86	$162.85	$162.90
7 purchase totals =	$1,141.52		$1,241.8887	$1,241.89	$1,241.85	$1,242.00