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	$83.29	8.801%	$90.6204	$90.62	$90.60	$90.60
Purchase #2	$127.67	9.459%	$139.7463	$139.75	$139.75	$139.70
Purchase #3	$74.32	5.443%	$78.3652	$78.37	$78.35	$78.40
Purchase #4	$48.58	4.712%	$50.8691	$50.87	$50.85	$50.90
Purchase #5	$170.45	6.643%	$181.773	$181.77	$181.75	$181.80
Purchase #6	$165.85	13.661%	$188.5068	$188.51	$188.50	$188.50
Purchase #7	$44.86	7.677%	$48.3039	$48.30	$48.30	$48.30
7 purchase totals =	$715.02		$778.1847	$778.19	$778.10	$778.20