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	$12.79	7.117%	$13.7003	$13.70	$13.70	$13.70
Purchase #2	$180.77	11.687%	$201.8966	$201.90	$201.90	$201.90
Purchase #3	$223.52	10.263%	$246.4599	$246.46	$246.45	$246.50
Purchase #4	$61.56	10.304%	$67.9031	$67.90	$67.90	$67.90
Purchase #5	$66.42	7.450%	$71.3683	$71.37	$71.35	$71.40
Purchase #6	$204.89	10.235%	$225.8605	$225.86	$225.85	$225.90
Purchase #7	$116.27	13.726%	$132.2292	$132.23	$132.25	$132.20
7 purchase totals =	$866.22		$959.4179	$959.42	$959.40	$959.50