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	$228.54	5.396%	$240.872	$240.87	$240.85	$240.90
Purchase #2	$155.45	4.340%	$162.1965	$162.20	$162.20	$162.20
Purchase #3	$156.35	10.808%	$173.2483	$173.25	$173.25	$173.20
Purchase #4	$102.37	3.143%	$105.5875	$105.59	$105.60	$105.60
Purchase #5	$29.43	9.458%	$32.2135	$32.21	$32.20	$32.20
Purchase #6	$79.81	3.774%	$82.822	$82.82	$82.80	$82.80
Purchase #7	$105.73	7.535%	$113.6968	$113.70	$113.70	$113.70
7 purchase totals =	$857.68		$910.6366	$910.64	$910.60	$910.60