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	$101.95	5.610%	$107.6694	$107.67	$107.65	$107.70
Purchase #2	$55.42	11.612%	$61.8554	$61.86	$61.85	$61.90
Purchase #3	$52.60	8.322%	$56.9774	$56.98	$57.00	$57.00
Purchase #4	$177.69	10.225%	$195.8588	$195.86	$195.85	$195.90
Purchase #5	$43.38	4.365%	$45.2735	$45.27	$45.25	$45.30
Purchase #6	$246.35	12.106%	$276.1731	$276.17	$276.15	$276.20
Purchase #7	$94.92	4.867%	$99.5398	$99.54	$99.55	$99.50
7 purchase totals =	$772.31		$843.3474	$843.35	$843.30	$843.50