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	$134.54	12.364%	$151.1745	$151.17	$151.15	$151.20
Purchase #2	$132.40	3.678%	$137.2697	$137.27	$137.25	$137.30
Purchase #3	$115.76	9.781%	$127.0825	$127.08	$127.10	$127.10
Purchase #4	$91.32	7.642%	$98.2987	$98.30	$98.30	$98.30
Purchase #5	$190.37	11.732%	$212.7042	$212.70	$212.70	$212.70
Purchase #6	$36.45	11.204%	$40.5339	$40.53	$40.55	$40.50
Purchase #7	$34.53	12.305%	$38.7789	$38.78	$38.80	$38.80
7 purchase totals =	$735.37		$805.8424	$805.83	$805.85	$805.90