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	$9.34	12.210%	$10.4804	$10.48	$10.50	$10.50
Purchase #2	$36.40	5.770%	$38.5003	$38.50	$38.50	$38.50
Purchase #3	$107.42	3.634%	$111.3236	$111.32	$111.30	$111.30
Purchase #4	$73.82	4.445%	$77.1013	$77.10	$77.10	$77.10
Purchase #5	$181.51	13.763%	$206.4912	$206.49	$206.50	$206.50
Purchase #6	$86.51	8.348%	$93.7319	$93.73	$93.75	$93.70
Purchase #7	$148.39	13.529%	$168.4657	$168.47	$168.45	$168.50
7 purchase totals =	$643.39		$706.0944	$706.09	$706.10	$706.10