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	$111.94	3.199%	$115.521	$115.52	$115.50	$115.50
Purchase #2	$111.88	13.555%	$127.0453	$127.05	$127.05	$127.00
Purchase #3	$187.64	7.591%	$201.8838	$201.88	$201.90	$201.90
Purchase #4	$47.95	5.540%	$50.6064	$50.61	$50.60	$50.60
Purchase #5	$123.36	12.615%	$138.9219	$138.92	$138.90	$138.90
Purchase #6	$104.45	6.309%	$111.0398	$111.04	$111.05	$111.00
Purchase #7	$181.92	5.445%	$191.8255	$191.83	$191.85	$191.80
7 purchase totals =	$869.14		$936.8437	$936.85	$936.85	$936.70