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	$58.79	13.577%	$66.7719	$66.77	$66.75	$66.80
Purchase #2	$34.95	8.194%	$37.8138	$37.81	$37.80	$37.80
Purchase #3	$52.43	13.329%	$59.4184	$59.42	$59.40	$59.40
Purchase #4	$37.38	4.682%	$39.1301	$39.13	$39.15	$39.10
Purchase #5	$184.35	11.322%	$205.2221	$205.22	$205.20	$205.20
Purchase #6	$39.27	7.739%	$42.3091	$42.31	$42.30	$42.30
Purchase #7	$161.67	12.421%	$181.751	$181.75	$181.75	$181.80
7 purchase totals =	$568.84		$632.4164	$632.41	$632.35	$632.40