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	$37.28	5.727%	$39.415	$39.42	$39.40	$39.40
Purchase #2	$246.81	3.408%	$255.2213	$255.22	$255.20	$255.20
Purchase #3	$24.61	9.174%	$26.8677	$26.87	$26.85	$26.90
Purchase #4	$222.56	11.391%	$247.9118	$247.91	$247.90	$247.90
Purchase #5	$188.78	4.312%	$196.9202	$196.92	$196.90	$196.90
Purchase #6	$117.49	8.386%	$127.3427	$127.34	$127.35	$127.30
Purchase #7	$100.71	11.225%	$112.0147	$112.01	$112.00	$112.00
7 purchase totals =	$938.24		$1,005.6934	$1,005.69	$1,005.60	$1,005.60