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	$198.51	7.537%	$213.4717	$213.47	$213.45	$213.50
Purchase #2	$38.78	9.658%	$42.5254	$42.53	$42.55	$42.50
Purchase #3	$237.68	8.401%	$257.6475	$257.65	$257.65	$257.60
Purchase #4	$53.75	5.788%	$56.8611	$56.86	$56.85	$56.90
Purchase #5	$78.73	4.509%	$82.2799	$82.28	$82.30	$82.30
Purchase #6	$125.31	11.288%	$139.455	$139.46	$139.45	$139.50
Purchase #7	$153.42	8.239%	$166.0603	$166.06	$166.05	$166.10
7 purchase totals =	$886.18		$958.3009	$958.31	$958.30	$958.40