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	$111.86	10.103%	$123.1612	$123.16	$123.15	$123.20
Purchase #2	$142.80	4.689%	$149.4959	$149.50	$149.50	$149.50
Purchase #3	$105.39	9.256%	$115.1449	$115.14	$115.15	$115.10
Purchase #4	$154.83	7.261%	$166.0722	$166.07	$166.05	$166.10
Purchase #5	$240.49	11.350%	$267.7856	$267.79	$267.80	$267.80
Purchase #6	$18.90	5.857%	$20.007	$20.01	$20.00	$20.00
Purchase #7	$127.45	11.496%	$142.1017	$142.10	$142.10	$142.10
7 purchase totals =	$901.72		$983.7685	$983.77	$983.75	$983.80