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	$106.87	7.501%	$114.8863	$114.89	$114.90	$114.90
Purchase #2	$37.76	6.660%	$40.2748	$40.27	$40.25	$40.30
Purchase #3	$19.37	10.186%	$21.343	$21.34	$21.35	$21.30
Purchase #4	$130.70	10.416%	$144.3137	$144.31	$144.30	$144.30
Purchase #5	$221.55	13.712%	$251.9289	$251.93	$251.95	$251.90
Purchase #6	$189.95	5.707%	$200.7904	$200.79	$200.80	$200.80
Purchase #7	$112.84	3.398%	$116.6743	$116.67	$116.65	$116.70
7 purchase totals =	$819.04		$890.2114	$890.20	$890.20	$890.20