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	$35.32	12.261%	$39.6506	$39.65	$39.65	$39.70
Purchase #2	$118.80	7.141%	$127.2835	$127.28	$127.30	$127.30
Purchase #3	$88.68	13.742%	$100.8664	$100.87	$100.85	$100.90
Purchase #4	$107.83	9.814%	$118.4124	$118.41	$118.40	$118.40
Purchase #5	$178.88	11.440%	$199.3439	$199.34	$199.35	$199.30
Purchase #6	$81.48	5.283%	$85.7846	$85.78	$85.80	$85.80
Purchase #7	$133.52	8.777%	$145.2391	$145.24	$145.25	$145.20
7 purchase totals =	$744.51		$816.5805	$816.57	$816.60	$816.60