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	$172.93	13.631%	$196.5021	$196.50	$196.50	$196.50
Purchase #2	$231.79	11.225%	$257.8084	$257.81	$257.80	$257.80
Purchase #3	$194.60	13.829%	$221.5112	$221.51	$221.50	$221.50
Purchase #4	$218.38	9.828%	$239.8424	$239.84	$239.85	$239.80
Purchase #5	$131.62	3.794%	$136.6137	$136.61	$136.60	$136.60
Purchase #6	$234.56	8.740%	$255.0605	$255.06	$255.05	$255.10
Purchase #7	$183.95	5.104%	$193.3388	$193.34	$193.35	$193.30
7 purchase totals =	$1,367.83		$1,500.6771	$1,500.67	$1,500.65	$1,500.60