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	$231.71	10.854%	$256.8598	$256.86	$256.85	$256.90
Purchase #2	$108.26	13.741%	$123.136	$123.14	$123.15	$123.10
Purchase #3	$171.75	4.682%	$179.7913	$179.79	$179.80	$179.80
Purchase #4	$121.31	3.320%	$125.3375	$125.34	$125.35	$125.30
Purchase #5	$184.35	13.500%	$209.2373	$209.24	$209.25	$209.20
Purchase #6	$241.71	11.624%	$269.8064	$269.81	$269.80	$269.80
Purchase #7	$143.43	5.853%	$151.825	$151.83	$151.85	$151.80
7 purchase totals =	$1,202.52		$1,315.9933	$1,316.01	$1,316.05	$1,315.90