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	$241.33	12.528%	$271.5638	$271.56	$271.55	$271.60
Purchase #2	$34.43	9.810%	$37.8076	$37.81	$37.80	$37.80
Purchase #3	$35.37	8.501%	$38.3768	$38.38	$38.40	$38.40
Purchase #4	$87.85	3.291%	$90.7411	$90.74	$90.75	$90.70
Purchase #5	$71.48	6.117%	$75.8524	$75.85	$75.85	$75.90
Purchase #6	$143.94	7.571%	$154.8377	$154.84	$154.85	$154.80
Purchase #7	$160.82	3.720%	$166.8025	$166.80	$166.80	$166.80
7 purchase totals =	$775.22		$835.9819	$835.98	$836.00	$836.00