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	$167.97	6.442%	$178.7906	$178.79	$178.80	$178.80
Purchase #2	$103.64	8.152%	$112.0887	$112.09	$112.10	$112.10
Purchase #3	$89.63	12.465%	$100.8024	$100.80	$100.80	$100.80
Purchase #4	$134.85	5.833%	$142.7158	$142.72	$142.70	$142.70
Purchase #5	$238.93	11.538%	$266.4977	$266.50	$266.50	$266.50
Purchase #6	$246.33	5.275%	$259.3239	$259.32	$259.30	$259.30
Purchase #7	$41.52	5.618%	$43.8526	$43.85	$43.85	$43.90
7 purchase totals =	$1,022.87		$1,104.0717	$1,104.07	$1,104.05	$1,104.10