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	$24.75	12.137%	$27.7539	$27.75	$27.75	$27.80
Purchase #2	$56.54	4.151%	$58.887	$58.89	$58.90	$58.90
Purchase #3	$56.35	10.211%	$62.1039	$62.10	$62.10	$62.10
Purchase #4	$37.32	12.848%	$42.1149	$42.11	$42.10	$42.10
Purchase #5	$238.94	3.189%	$246.5598	$246.56	$246.55	$246.60
Purchase #6	$147.43	7.376%	$158.3044	$158.30	$158.30	$158.30
Purchase #7	$139.53	10.147%	$153.6881	$153.69	$153.70	$153.70
7 purchase totals =	$700.86		$749.4120	$749.40	$749.40	$749.50