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	$83.38	11.403%	$92.8878	$92.89	$92.90	$92.90
Purchase #2	$81.39	7.404%	$87.4161	$87.42	$87.40	$87.40
Purchase #3	$137.81	4.846%	$144.4883	$144.49	$144.50	$144.50
Purchase #4	$94.85	10.699%	$104.998	$105.00	$105.00	$105.00
Purchase #5	$94.65	3.583%	$98.0413	$98.04	$98.05	$98.00
Purchase #6	$100.58	4.498%	$105.1041	$105.10	$105.10	$105.10
Purchase #7	$122.49	4.320%	$127.7816	$127.78	$127.80	$127.80
7 purchase totals =	$715.15		$760.7172	$760.72	$760.75	$760.70