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	$77.60	4.462%	$81.0625	$81.06	$81.05	$81.10
Purchase #2	$57.79	7.741%	$62.2635	$62.26	$62.25	$62.30
Purchase #3	$225.43	7.304%	$241.8954	$241.90	$241.90	$241.90
Purchase #4	$151.87	9.174%	$165.8026	$165.80	$165.80	$165.80
Purchase #5	$90.32	5.531%	$95.3156	$95.32	$95.30	$95.30
Purchase #6	$213.83	8.416%	$231.8259	$231.83	$231.85	$231.80
Purchase #7	$86.87	5.641%	$91.7703	$91.77	$91.75	$91.80
7 purchase totals =	$903.71		$969.9358	$969.94	$969.90	$970.00