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	$238.50	8.352%	$258.4195	$258.42	$258.40	$258.40
Purchase #2	$247.32	7.826%	$266.6753	$266.68	$266.70	$266.70
Purchase #3	$124.98	11.435%	$139.2715	$139.27	$139.25	$139.30
Purchase #4	$88.70	8.229%	$95.9991	$96.00	$96.00	$96.00
Purchase #5	$150.52	10.716%	$166.6497	$166.65	$166.65	$166.60
Purchase #6	$114.42	11.734%	$127.846	$127.85	$127.85	$127.80
Purchase #7	$84.31	7.500%	$90.6333	$90.63	$90.65	$90.60
7 purchase totals =	$1,048.75		$1,145.4944	$1,145.50	$1,145.50	$1,145.40