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	$71.55	9.869%	$78.6113	$78.61	$78.60	$78.60
Purchase #2	$83.48	11.590%	$93.1553	$93.16	$93.15	$93.20
Purchase #3	$168.73	6.699%	$180.0332	$180.03	$180.05	$180.00
Purchase #4	$241.29	7.473%	$259.3216	$259.32	$259.30	$259.30
Purchase #5	$233.52	10.258%	$257.4745	$257.47	$257.45	$257.50
Purchase #6	$55.51	3.548%	$57.4795	$57.48	$57.50	$57.50
Purchase #7	$194.54	5.423%	$205.0899	$205.09	$205.10	$205.10
7 purchase totals =	$1,048.62		$1,131.1653	$1,131.16	$1,131.15	$1,131.20