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	$246.54	12.102%	$276.3763	$276.38	$276.40	$276.40
Purchase #2	$127.71	8.679%	$138.794	$138.79	$138.80	$138.80
Purchase #3	$182.33	13.307%	$206.5927	$206.59	$206.60	$206.60
Purchase #4	$177.88	8.269%	$192.5889	$192.59	$192.60	$192.60
Purchase #5	$152.77	12.275%	$171.5225	$171.52	$171.50	$171.50
Purchase #6	$141.38	13.283%	$160.1595	$160.16	$160.15	$160.20
Purchase #7	$73.51	4.551%	$76.8554	$76.86	$76.85	$76.90
7 purchase totals =	$1,102.12		$1,222.8893	$1,222.89	$1,222.90	$1,223.00