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	$25.98	7.228%	$27.8578	$27.86	$27.85	$27.90
Purchase #2	$116.92	5.770%	$123.6663	$123.67	$123.65	$123.70
Purchase #3	$17.68	5.106%	$18.5827	$18.58	$18.60	$18.60
Purchase #4	$228.29	12.527%	$256.8879	$256.89	$256.90	$256.90
Purchase #5	$147.92	5.163%	$155.5571	$155.56	$155.55	$155.60
Purchase #6	$69.88	13.749%	$79.4878	$79.49	$79.50	$79.50
Purchase #7	$101.61	4.722%	$106.408	$106.41	$106.40	$106.40
7 purchase totals =	$708.28		$768.4476	$768.46	$768.45	$768.60