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	$130.66	13.584%	$148.4089	$148.41	$148.40	$148.40
Purchase #2	$167.58	8.640%	$182.0589	$182.06	$182.05	$182.10
Purchase #3	$46.70	10.502%	$51.6044	$51.60	$51.60	$51.60
Purchase #4	$116.89	9.388%	$127.8636	$127.86	$127.85	$127.90
Purchase #5	$146.92	12.373%	$165.0984	$165.10	$165.10	$165.10
Purchase #6	$166.60	13.228%	$188.6378	$188.64	$188.65	$188.60
Purchase #7	$50.94	6.819%	$54.4136	$54.41	$54.40	$54.40
7 purchase totals =	$826.29		$918.0856	$918.08	$918.05	$918.10