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	$134.96	8.382%	$146.2723	$146.27	$146.25	$146.30
Purchase #2	$74.39	11.305%	$82.7998	$82.80	$82.80	$82.80
Purchase #3	$49.72	5.666%	$52.5371	$52.54	$52.55	$52.50
Purchase #4	$121.42	12.767%	$136.9217	$136.92	$136.90	$136.90
Purchase #5	$84.60	11.858%	$94.6319	$94.63	$94.65	$94.60
Purchase #6	$85.62	7.552%	$92.086	$92.09	$92.10	$92.10
Purchase #7	$34.43	11.367%	$38.3437	$38.34	$38.35	$38.30
7 purchase totals =	$585.14		$643.5925	$643.59	$643.60	$643.50