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	$34.77	11.461%	$38.755	$38.76	$38.75	$38.80
Purchase #2	$71.29	8.387%	$77.2691	$77.27	$77.25	$77.30
Purchase #3	$29.52	13.143%	$33.3998	$33.40	$33.40	$33.40
Purchase #4	$94.97	8.856%	$103.3805	$103.38	$103.40	$103.40
Purchase #5	$105.34	5.626%	$111.2664	$111.27	$111.25	$111.30
Purchase #6	$36.51	12.409%	$41.0405	$41.04	$41.05	$41.00
Purchase #7	$176.91	6.480%	$188.3738	$188.37	$188.35	$188.40
7 purchase totals =	$549.31		$593.4851	$593.49	$593.45	$593.60