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	$58.91	12.617%	$66.3427	$66.34	$66.35	$66.30
Purchase #2	$151.54	6.755%	$161.7765	$161.78	$161.80	$161.80
Purchase #3	$63.78	11.814%	$71.315	$71.32	$71.30	$71.30
Purchase #4	$55.27	13.123%	$62.5231	$62.52	$62.50	$62.50
Purchase #5	$144.41	6.463%	$153.7432	$153.74	$153.75	$153.70
Purchase #6	$148.73	11.763%	$166.2251	$166.23	$166.25	$166.20
Purchase #7	$45.79	6.798%	$48.9028	$48.90	$48.90	$48.90
7 purchase totals =	$668.43		$730.8284	$730.83	$730.85	$730.70