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	$38.53	3.328%	$39.8123	$39.81	$39.80	$39.80
Purchase #2	$184.40	12.581%	$207.5994	$207.60	$207.60	$207.60
Purchase #3	$85.88	12.391%	$96.5214	$96.52	$96.50	$96.50
Purchase #4	$175.85	9.849%	$193.1695	$193.17	$193.15	$193.20
Purchase #5	$123.45	11.166%	$137.2344	$137.23	$137.25	$137.20
Purchase #6	$133.62	6.383%	$142.149	$142.15	$142.15	$142.10
Purchase #7	$18.27	10.358%	$20.1624	$20.16	$20.15	$20.20
7 purchase totals =	$760.00		$836.6484	$836.64	$836.60	$836.60