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	$16.30	12.577%	$18.3501	$18.35	$18.35	$18.40
Purchase #2	$36.74	3.719%	$38.1064	$38.11	$38.10	$38.10
Purchase #3	$67.94	4.378%	$70.9144	$70.91	$70.90	$70.90
Purchase #4	$108.36	3.770%	$112.4452	$112.45	$112.45	$112.40
Purchase #5	$205.82	13.376%	$233.3505	$233.35	$233.35	$233.40
Purchase #6	$18.90	6.680%	$20.1625	$20.16	$20.15	$20.20
Purchase #7	$31.78	5.363%	$33.4844	$33.48	$33.50	$33.50
7 purchase totals =	$485.84		$526.8135	$526.81	$526.80	$526.90