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	$17.40	12.791%	$19.6256	$19.63	$19.65	$19.60
Purchase #2	$159.39	8.129%	$172.3468	$172.35	$172.35	$172.30
Purchase #3	$113.55	6.484%	$120.9126	$120.91	$120.90	$120.90
Purchase #4	$241.52	9.115%	$263.5345	$263.53	$263.55	$263.50
Purchase #5	$158.43	10.167%	$174.5376	$174.54	$174.55	$174.50
Purchase #6	$250.47	5.722%	$264.8019	$264.80	$264.80	$264.80
Purchase #7	$75.88	10.583%	$83.9104	$83.91	$83.90	$83.90
7 purchase totals =	$1,016.64		$1,099.6694	$1,099.67	$1,099.70	$1,099.50