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	$78.98	4.528%	$82.5562	$82.56	$82.55	$82.60
Purchase #2	$11.38	8.576%	$12.3559	$12.36	$12.35	$12.40
Purchase #3	$186.58	7.434%	$200.4504	$200.45	$200.45	$200.50
Purchase #4	$48.64	12.128%	$54.5391	$54.54	$54.55	$54.50
Purchase #5	$113.39	7.830%	$122.2684	$122.27	$122.25	$122.30
Purchase #6	$61.71	12.754%	$69.5805	$69.58	$69.60	$69.60
Purchase #7	$66.38	11.272%	$73.8624	$73.86	$73.85	$73.90
7 purchase totals =	$567.06		$615.6129	$615.62	$615.60	$615.80