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	$46.94	8.487%	$50.9238	$50.92	$50.90	$50.90
Purchase #2	$95.77	13.463%	$108.6635	$108.66	$108.65	$108.70
Purchase #3	$185.34	6.264%	$196.9497	$196.95	$196.95	$196.90
Purchase #4	$177.41	7.426%	$190.5845	$190.58	$190.60	$190.60
Purchase #5	$53.34	5.174%	$56.0998	$56.10	$56.10	$56.10
Purchase #6	$210.91	13.314%	$238.9906	$238.99	$239.00	$239.00
Purchase #7	$82.68	3.286%	$85.3969	$85.40	$85.40	$85.40
7 purchase totals =	$852.39		$927.6088	$927.60	$927.60	$927.60