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	$128.54	9.147%	$140.2976	$140.30	$140.30	$140.30
Purchase #2	$62.38	9.786%	$68.4845	$68.48	$68.50	$68.50
Purchase #3	$168.27	11.605%	$187.7977	$187.80	$187.80	$187.80
Purchase #4	$95.39	10.521%	$105.426	$105.43	$105.45	$105.40
Purchase #5	$134.30	9.863%	$147.546	$147.55	$147.55	$147.50
Purchase #6	$91.90	13.217%	$104.0464	$104.05	$104.05	$104.00
Purchase #7	$38.89	3.322%	$40.1819	$40.18	$40.20	$40.20
7 purchase totals =	$719.67		$793.7801	$793.79	$793.85	$793.70