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	$245.49	13.434%	$278.4691	$278.47	$278.45	$278.50
Purchase #2	$121.59	13.661%	$138.2004	$138.20	$138.20	$138.20
Purchase #3	$216.46	8.128%	$234.0539	$234.05	$234.05	$234.10
Purchase #4	$99.94	11.443%	$111.3761	$111.38	$111.40	$111.40
Purchase #5	$42.59	6.610%	$45.4052	$45.41	$45.40	$45.40
Purchase #6	$177.30	3.579%	$183.6456	$183.65	$183.65	$183.60
Purchase #7	$74.37	10.103%	$81.8836	$81.88	$81.90	$81.90
7 purchase totals =	$977.74		$1,073.0339	$1,073.04	$1,073.05	$1,073.10