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	$203.95	5.560%	$215.2896	$215.29	$215.30	$215.30
Purchase #2	$150.82	5.653%	$159.3459	$159.35	$159.35	$159.30
Purchase #3	$240.89	7.531%	$259.0314	$259.03	$259.05	$259.00
Purchase #4	$52.60	5.693%	$55.5945	$55.59	$55.60	$55.60
Purchase #5	$93.77	7.173%	$100.4961	$100.50	$100.50	$100.50
Purchase #6	$90.93	5.612%	$96.033	$96.03	$96.05	$96.00
Purchase #7	$65.45	7.609%	$70.4301	$70.43	$70.45	$70.40
7 purchase totals =	$898.41		$956.2206	$956.22	$956.30	$956.10