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	$40.52	13.481%	$45.9825	$45.98	$46.00	$46.00
Purchase #2	$134.90	5.155%	$141.8541	$141.85	$141.85	$141.90
Purchase #3	$106.40	9.600%	$116.6144	$116.61	$116.60	$116.60
Purchase #4	$135.78	12.679%	$152.9955	$153.00	$153.00	$153.00
Purchase #5	$130.35	3.347%	$134.7128	$134.71	$134.70	$134.70
Purchase #6	$90.83	4.612%	$95.0191	$95.02	$95.00	$95.00
Purchase #7	$39.90	9.547%	$43.7093	$43.71	$43.70	$43.70
7 purchase totals =	$678.68		$730.8877	$730.88	$730.85	$730.90