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	$83.99	6.754%	$89.6627	$89.66	$89.65	$89.70
Purchase #2	$174.69	10.176%	$192.4665	$192.47	$192.45	$192.50
Purchase #3	$112.75	12.750%	$127.1256	$127.13	$127.15	$127.10
Purchase #4	$40.80	5.519%	$43.0518	$43.05	$43.05	$43.10
Purchase #5	$75.72	13.852%	$86.2087	$86.21	$86.20	$86.20
Purchase #6	$114.58	8.301%	$124.0913	$124.09	$124.10	$124.10
Purchase #7	$210.80	12.746%	$237.6686	$237.67	$237.65	$237.70
7 purchase totals =	$813.33		$900.2752	$900.28	$900.25	$900.40