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	$20.62	4.182%	$21.4823	$21.48	$21.50	$21.50
Purchase #2	$127.89	13.321%	$144.9262	$144.93	$144.95	$144.90
Purchase #3	$138.82	9.487%	$151.9899	$151.99	$152.00	$152.00
Purchase #4	$160.61	5.398%	$169.2797	$169.28	$169.30	$169.30
Purchase #5	$152.44	9.785%	$167.3563	$167.36	$167.35	$167.40
Purchase #6	$136.39	11.715%	$152.3681	$152.37	$152.35	$152.40
Purchase #7	$116.37	5.704%	$123.0077	$123.01	$123.00	$123.00
7 purchase totals =	$853.14		$930.4102	$930.42	$930.45	$930.50