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	$227.79	13.423%	$258.3663	$258.37	$258.35	$258.40
Purchase #2	$78.92	4.677%	$82.6111	$82.61	$82.60	$82.60
Purchase #3	$242.40	12.229%	$272.0431	$272.04	$272.05	$272.00
Purchase #4	$243.49	7.124%	$260.8362	$260.84	$260.85	$260.80
Purchase #5	$90.53	9.855%	$99.4517	$99.45	$99.45	$99.50
Purchase #6	$195.35	11.126%	$217.0846	$217.08	$217.10	$217.10
Purchase #7	$46.72	9.233%	$51.0337	$51.03	$51.05	$51.00
7 purchase totals =	$1,125.20		$1,241.4267	$1,241.42	$1,241.45	$1,241.40