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	$140.79	10.286%	$155.2717	$155.27	$155.25	$155.30
Purchase #2	$89.32	7.292%	$95.8332	$95.83	$95.85	$95.80
Purchase #3	$156.98	6.381%	$166.9969	$167.00	$167.00	$167.00
Purchase #4	$15.34	6.217%	$16.2937	$16.29	$16.30	$16.30
Purchase #5	$11.99	13.470%	$13.6051	$13.61	$13.60	$13.60
Purchase #6	$239.49	6.531%	$255.1311	$255.13	$255.15	$255.10
Purchase #7	$78.90	9.409%	$86.3237	$86.32	$86.30	$86.30
7 purchase totals =	$732.81		$789.4554	$789.45	$789.45	$789.40