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	$62.59	6.768%	$66.8261	$66.83	$66.85	$66.80
Purchase #2	$147.34	3.461%	$152.4394	$152.44	$152.45	$152.40
Purchase #3	$203.91	12.102%	$228.5872	$228.59	$228.60	$228.60
Purchase #4	$60.54	11.572%	$67.5457	$67.55	$67.55	$67.50
Purchase #5	$189.82	7.784%	$204.5956	$204.60	$204.60	$204.60
Purchase #6	$99.73	3.316%	$103.037	$103.04	$103.05	$103.00
Purchase #7	$92.86	12.602%	$104.5622	$104.56	$104.55	$104.60
7 purchase totals =	$856.79		$927.5932	$927.61	$927.65	$927.50