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	$123.56	11.108%	$137.285	$137.29	$137.30	$137.30
Purchase #2	$176.28	13.689%	$200.411	$200.41	$200.40	$200.40
Purchase #3	$139.27	8.244%	$150.7514	$150.75	$150.75	$150.80
Purchase #4	$116.33	10.710%	$128.7889	$128.79	$128.80	$128.80
Purchase #5	$122.83	11.420%	$136.8572	$136.86	$136.85	$136.90
Purchase #6	$100.91	3.756%	$104.7002	$104.70	$104.70	$104.70
Purchase #7	$141.67	4.528%	$148.0848	$148.08	$148.10	$148.10
7 purchase totals =	$920.85		$1,006.8785	$1,006.88	$1,006.90	$1,007.00