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	$38.46	4.524%	$40.1999	$40.20	$40.20	$40.20
Purchase #2	$116.58	8.854%	$126.902	$126.90	$126.90	$126.90
Purchase #3	$141.81	11.827%	$158.5819	$158.58	$158.60	$158.60
Purchase #4	$86.82	12.342%	$97.5353	$97.54	$97.55	$97.50
Purchase #5	$80.65	13.168%	$91.27	$91.27	$91.25	$91.30
Purchase #6	$58.43	5.695%	$61.7576	$61.76	$61.75	$61.80
Purchase #7	$118.61	8.630%	$128.846	$128.85	$128.85	$128.80
7 purchase totals =	$641.36		$705.0927	$705.10	$705.10	$705.10