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	$106.79	13.316%	$121.0102	$121.01	$121.00	$121.00
Purchase #2	$143.25	5.838%	$151.6129	$151.61	$151.60	$151.60
Purchase #3	$248.58	12.180%	$278.857	$278.86	$278.85	$278.90
Purchase #4	$149.77	13.222%	$169.5726	$169.57	$169.55	$169.60
Purchase #5	$224.80	5.822%	$237.8879	$237.89	$237.90	$237.90
Purchase #6	$78.61	9.381%	$85.9844	$85.98	$86.00	$86.00
Purchase #7	$52.37	13.784%	$59.5887	$59.59	$59.60	$59.60
7 purchase totals =	$1,004.17		$1,104.5137	$1,104.51	$1,104.50	$1,104.60