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	$54.70	12.295%	$61.4254	$61.43	$61.45	$61.40
Purchase #2	$82.98	9.587%	$90.9353	$90.94	$90.95	$90.90
Purchase #3	$25.68	4.356%	$26.7986	$26.80	$26.80	$26.80
Purchase #4	$56.30	12.465%	$63.3178	$63.32	$63.30	$63.30
Purchase #5	$98.54	5.504%	$103.9636	$103.96	$103.95	$104.00
Purchase #6	$17.45	12.281%	$19.593	$19.59	$19.60	$19.60
Purchase #7	$191.60	8.849%	$208.5547	$208.55	$208.55	$208.60
7 purchase totals =	$527.25		$574.5884	$574.59	$574.60	$574.60