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	$137.56	11.697%	$153.6504	$153.65	$153.65	$153.70
Purchase #2	$99.75	9.371%	$109.0976	$109.10	$109.10	$109.10
Purchase #3	$18.90	13.402%	$21.433	$21.43	$21.45	$21.40
Purchase #4	$98.55	10.455%	$108.8534	$108.85	$108.85	$108.90
Purchase #5	$59.97	4.271%	$62.5313	$62.53	$62.55	$62.50
Purchase #6	$117.83	4.213%	$122.7942	$122.79	$122.80	$122.80
Purchase #7	$69.55	3.775%	$72.1755	$72.18	$72.20	$72.20
7 purchase totals =	$602.11		$650.5354	$650.53	$650.60	$650.60