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	$11.49	7.538%	$12.3561	$12.36	$12.35	$12.40
Purchase #2	$125.87	3.473%	$130.2415	$130.24	$130.25	$130.20
Purchase #3	$112.77	9.845%	$123.8722	$123.87	$123.85	$123.90
Purchase #4	$62.73	6.617%	$66.8808	$66.88	$66.90	$66.90
Purchase #5	$138.94	12.386%	$156.1491	$156.15	$156.15	$156.10
Purchase #6	$50.26	11.155%	$55.8665	$55.87	$55.85	$55.90
Purchase #7	$52.86	12.605%	$59.523	$59.52	$59.50	$59.50
7 purchase totals =	$554.92		$604.8892	$604.89	$604.85	$604.90