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	$105.39	12.321%	$118.3751	$118.38	$118.40	$118.40
Purchase #2	$94.35	11.402%	$105.1078	$105.11	$105.10	$105.10
Purchase #3	$202.55	6.311%	$215.3329	$215.33	$215.35	$215.30
Purchase #4	$81.89	13.773%	$93.1687	$93.17	$93.15	$93.20
Purchase #5	$41.97	3.167%	$43.2992	$43.30	$43.30	$43.30
Purchase #6	$34.33	12.434%	$38.5986	$38.60	$38.60	$38.60
Purchase #7	$242.75	6.133%	$257.6379	$257.64	$257.65	$257.60
7 purchase totals =	$803.23		$871.5202	$871.53	$871.55	$871.50