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	$166.26	11.628%	$185.5927	$185.59	$185.60	$185.60
Purchase #2	$240.38	10.476%	$265.5622	$265.56	$265.55	$265.60
Purchase #3	$162.46	9.286%	$177.546	$177.55	$177.55	$177.50
Purchase #4	$83.85	7.634%	$90.2511	$90.25	$90.25	$90.30
Purchase #5	$238.62	6.874%	$255.0227	$255.02	$255.00	$255.00
Purchase #6	$39.70	8.538%	$43.0896	$43.09	$43.10	$43.10
Purchase #7	$177.40	3.453%	$183.5256	$183.53	$183.55	$183.50
7 purchase totals =	$1,108.67		$1,200.5899	$1,200.59	$1,200.60	$1,200.60