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	$10.59	13.170%	$11.9847	$11.98	$12.00	$12.00
Purchase #2	$12.55	8.401%	$13.6043	$13.60	$13.60	$13.60
Purchase #3	$198.43	8.739%	$215.7708	$215.77	$215.75	$215.80
Purchase #4	$180.39	8.689%	$196.0641	$196.06	$196.05	$196.10
Purchase #5	$195.89	10.721%	$216.8914	$216.89	$216.90	$216.90
Purchase #6	$24.98	9.237%	$27.2874	$27.29	$27.30	$27.30
Purchase #7	$129.64	11.154%	$144.1	$144.10	$144.10	$144.10
7 purchase totals =	$752.47		$825.7027	$825.69	$825.70	$825.80