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	$243.30	5.767%	$257.3311	$257.33	$257.35	$257.30
Purchase #2	$162.78	4.609%	$170.2825	$170.28	$170.30	$170.30
Purchase #3	$52.63	13.219%	$59.5872	$59.59	$59.60	$59.60
Purchase #4	$219.59	13.791%	$249.8737	$249.87	$249.85	$249.90
Purchase #5	$99.78	9.158%	$108.9179	$108.92	$108.90	$108.90
Purchase #6	$90.86	5.236%	$95.6174	$95.62	$95.60	$95.60
Purchase #7	$218.68	10.350%	$241.3134	$241.31	$241.30	$241.30
7 purchase totals =	$1,087.62		$1,182.9232	$1,182.92	$1,182.90	$1,182.90