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	$245.99	12.205%	$276.0131	$276.01	$276.00	$276.00
Purchase #2	$127.35	9.619%	$139.5998	$139.60	$139.60	$139.60
Purchase #3	$91.66	10.851%	$101.606	$101.61	$101.60	$101.60
Purchase #4	$72.59	12.513%	$81.6732	$81.67	$81.65	$81.70
Purchase #5	$99.72	11.579%	$111.2666	$111.27	$111.25	$111.30
Purchase #6	$64.99	8.340%	$70.4102	$70.41	$70.40	$70.40
Purchase #7	$201.92	7.382%	$216.8257	$216.83	$216.85	$216.80
7 purchase totals =	$904.22		$997.3946	$997.40	$997.35	$997.40