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	$99.79	6.222%	$105.9989	$106.00	$106.00	$106.00
Purchase #2	$44.64	12.230%	$50.0995	$50.10	$50.10	$50.10
Purchase #3	$153.54	8.117%	$166.0028	$166.00	$166.00	$166.00
Purchase #4	$57.73	3.265%	$59.6149	$59.61	$59.60	$59.60
Purchase #5	$64.68	3.358%	$66.852	$66.85	$66.85	$66.90
Purchase #6	$239.39	10.871%	$265.4141	$265.41	$265.40	$265.40
Purchase #7	$56.27	10.869%	$62.386	$62.39	$62.40	$62.40
7 purchase totals =	$716.04		$776.3682	$776.36	$776.35	$776.40