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	$53.73	10.793%	$59.5291	$59.53	$59.55	$59.50
Purchase #2	$119.83	3.439%	$123.951	$123.95	$123.95	$124.00
Purchase #3	$91.66	12.624%	$103.2312	$103.23	$103.25	$103.20
Purchase #4	$63.82	3.398%	$65.9886	$65.99	$66.00	$66.00
Purchase #5	$60.40	5.106%	$63.484	$63.48	$63.50	$63.50
Purchase #6	$124.61	11.692%	$139.1794	$139.18	$139.20	$139.20
Purchase #7	$30.51	12.523%	$34.3308	$34.33	$34.35	$34.30
7 purchase totals =	$544.56		$589.6941	$589.69	$589.80	$589.70