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	$230.85	9.403%	$252.5568	$252.56	$252.55	$252.60
Purchase #2	$123.92	12.480%	$139.3852	$139.39	$139.40	$139.40
Purchase #3	$95.48	9.318%	$104.3768	$104.38	$104.40	$104.40
Purchase #4	$74.32	6.400%	$79.0765	$79.08	$79.10	$79.10
Purchase #5	$165.75	3.453%	$171.4733	$171.47	$171.45	$171.50
Purchase #6	$87.89	4.364%	$91.7255	$91.73	$91.75	$91.70
Purchase #7	$133.86	4.155%	$139.4219	$139.42	$139.40	$139.40
7 purchase totals =	$912.07		$978.0160	$978.03	$978.05	$978.10