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	$217.82	6.196%	$231.3161	$231.32	$231.30	$231.30
Purchase #2	$22.39	11.409%	$24.9445	$24.94	$24.95	$24.90
Purchase #3	$96.49	9.697%	$105.8466	$105.85	$105.85	$105.80
Purchase #4	$28.81	9.373%	$31.5104	$31.51	$31.50	$31.50
Purchase #5	$127.65	13.639%	$145.0602	$145.06	$145.05	$145.10
Purchase #6	$101.64	5.533%	$107.2637	$107.26	$107.25	$107.30
Purchase #7	$133.32	13.141%	$150.8396	$150.84	$150.85	$150.80
7 purchase totals =	$728.12		$796.7811	$796.78	$796.75	$796.70