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	$94.30	12.246%	$105.848	$105.85	$105.85	$105.80
Purchase #2	$179.31	5.595%	$189.3424	$189.34	$189.35	$189.30
Purchase #3	$35.72	10.873%	$39.6038	$39.60	$39.60	$39.60
Purchase #4	$100.81	7.334%	$108.2034	$108.20	$108.20	$108.20
Purchase #5	$141.38	3.625%	$146.505	$146.51	$146.50	$146.50
Purchase #6	$244.49	6.298%	$259.888	$259.89	$259.90	$259.90
Purchase #7	$103.69	10.348%	$114.4198	$114.42	$114.40	$114.40
7 purchase totals =	$899.70		$963.8104	$963.81	$963.80	$963.70