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	$24.68	11.354%	$27.4822	$27.48	$27.50	$27.50
Purchase #2	$167.44	9.387%	$183.1576	$183.16	$183.15	$183.20
Purchase #3	$220.37	11.584%	$245.8977	$245.90	$245.90	$245.90
Purchase #4	$104.43	6.432%	$111.1469	$111.15	$111.15	$111.10
Purchase #5	$171.74	5.452%	$181.1033	$181.10	$181.10	$181.10
Purchase #6	$51.39	7.349%	$55.1667	$55.17	$55.15	$55.20
Purchase #7	$12.37	8.810%	$13.4598	$13.46	$13.45	$13.50
7 purchase totals =	$752.42		$817.4142	$817.42	$817.40	$817.50