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	$242.66	5.298%	$255.5161	$255.52	$255.50	$255.50
Purchase #2	$130.72	11.398%	$145.6195	$145.62	$145.60	$145.60
Purchase #3	$74.31	4.671%	$77.781	$77.78	$77.80	$77.80
Purchase #4	$111.54	12.827%	$125.8472	$125.85	$125.85	$125.80
Purchase #5	$177.65	11.681%	$198.4013	$198.40	$198.40	$198.40
Purchase #6	$56.50	5.578%	$59.6516	$59.65	$59.65	$59.70
Purchase #7	$73.92	7.737%	$79.6392	$79.64	$79.65	$79.60
7 purchase totals =	$867.30		$942.4559	$942.46	$942.45	$942.40