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	$38.52	8.430%	$41.7672	$41.77	$41.75	$41.80
Purchase #2	$55.66	11.821%	$62.2396	$62.24	$62.25	$62.20
Purchase #3	$129.56	3.792%	$134.4729	$134.47	$134.45	$134.50
Purchase #4	$73.88	5.442%	$77.9005	$77.90	$77.90	$77.90
Purchase #5	$215.91	11.754%	$241.2881	$241.29	$241.30	$241.30
Purchase #6	$22.57	12.147%	$25.3116	$25.31	$25.30	$25.30
Purchase #7	$51.41	10.676%	$56.8985	$56.90	$56.90	$56.90
7 purchase totals =	$587.51		$639.8784	$639.88	$639.85	$639.90