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	$50.77	6.513%	$54.0767	$54.08	$54.10	$54.10
Purchase #2	$59.38	5.804%	$62.8264	$62.83	$62.85	$62.80
Purchase #3	$95.66	12.353%	$107.4769	$107.48	$107.50	$107.50
Purchase #4	$124.53	13.211%	$140.9817	$140.98	$141.00	$141.00
Purchase #5	$54.55	6.440%	$58.063	$58.06	$58.05	$58.10
Purchase #6	$80.78	5.782%	$85.4507	$85.45	$85.45	$85.50
Purchase #7	$116.82	4.619%	$122.2159	$122.22	$122.20	$122.20
7 purchase totals =	$582.49		$631.0913	$631.10	$631.15	$631.20