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	$203.39	4.150%	$211.8307	$211.83	$211.85	$211.80
Purchase #2	$154.52	13.587%	$175.5146	$175.51	$175.50	$175.50
Purchase #3	$105.59	13.288%	$119.6208	$119.62	$119.60	$119.60
Purchase #4	$82.82	13.841%	$94.2831	$94.28	$94.30	$94.30
Purchase #5	$162.45	10.385%	$179.3204	$179.32	$179.30	$179.30
Purchase #6	$126.29	9.750%	$138.6033	$138.60	$138.60	$138.60
Purchase #7	$41.40	10.508%	$45.7503	$45.75	$45.75	$45.80
7 purchase totals =	$876.46		$964.9232	$964.91	$964.90	$964.90