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	$240.80	13.776%	$273.9726	$273.97	$273.95	$274.00
Purchase #2	$174.75	8.464%	$189.5408	$189.54	$189.55	$189.50
Purchase #3	$48.80	10.610%	$53.9777	$53.98	$54.00	$54.00
Purchase #4	$37.70	7.678%	$40.5946	$40.59	$40.60	$40.60
Purchase #5	$198.61	9.485%	$217.4482	$217.45	$217.45	$217.40
Purchase #6	$143.82	5.174%	$151.2612	$151.26	$151.25	$151.30
Purchase #7	$131.92	6.834%	$140.9354	$140.94	$140.95	$140.90
7 purchase totals =	$976.40		$1,067.7305	$1,067.73	$1,067.75	$1,067.70