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	$108.77	12.528%	$122.3967	$122.40	$122.40	$122.40
Purchase #2	$184.91	3.443%	$191.2765	$191.28	$191.30	$191.30
Purchase #3	$204.72	4.248%	$213.4165	$213.42	$213.40	$213.40
Purchase #4	$71.36	12.585%	$80.3407	$80.34	$80.35	$80.30
Purchase #5	$217.35	5.569%	$229.4542	$229.45	$229.45	$229.50
Purchase #6	$156.57	7.589%	$168.4521	$168.45	$168.45	$168.50
Purchase #7	$193.35	12.353%	$217.2345	$217.23	$217.25	$217.20
7 purchase totals =	$1,137.03		$1,222.5712	$1,222.57	$1,222.60	$1,222.60