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	$66.83	12.179%	$74.9692	$74.97	$74.95	$75.00
Purchase #2	$98.83	12.740%	$111.4209	$111.42	$111.40	$111.40
Purchase #3	$94.91	9.655%	$104.0736	$104.07	$104.05	$104.10
Purchase #4	$94.64	9.836%	$103.9488	$103.95	$103.95	$103.90
Purchase #5	$88.32	4.536%	$92.3262	$92.33	$92.35	$92.30
Purchase #6	$156.72	5.729%	$165.6985	$165.70	$165.70	$165.70
Purchase #7	$114.74	10.850%	$127.1893	$127.19	$127.20	$127.20
7 purchase totals =	$714.99		$779.6265	$779.63	$779.60	$779.60