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	$58.49	13.767%	$66.5423	$66.54	$66.55	$66.50
Purchase #2	$24.47	13.554%	$27.7867	$27.79	$27.80	$27.80
Purchase #3	$101.66	5.473%	$107.2239	$107.22	$107.20	$107.20
Purchase #4	$40.86	12.155%	$45.8265	$45.83	$45.85	$45.80
Purchase #5	$88.93	12.749%	$100.2677	$100.27	$100.25	$100.30
Purchase #6	$95.91	13.328%	$108.6929	$108.69	$108.70	$108.70
Purchase #7	$106.83	12.729%	$120.4284	$120.43	$120.45	$120.40
7 purchase totals =	$517.15		$576.7684	$576.77	$576.80	$576.70