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	$81.81	10.796%	$90.6422	$90.64	$90.65	$90.60
Purchase #2	$89.53	12.604%	$100.8144	$100.81	$100.80	$100.80
Purchase #3	$133.47	13.672%	$151.718	$151.72	$151.70	$151.70
Purchase #4	$84.47	7.239%	$90.5848	$90.58	$90.60	$90.60
Purchase #5	$97.97	5.569%	$103.4259	$103.43	$103.45	$103.40
Purchase #6	$224.93	9.279%	$245.8013	$245.80	$245.80	$245.80
Purchase #7	$26.35	11.340%	$29.3381	$29.34	$29.35	$29.30
7 purchase totals =	$738.53		$812.3247	$812.32	$812.35	$812.20