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	$10.84	13.813%	$12.3373	$12.34	$12.35	$12.30
Purchase #2	$92.33	12.563%	$103.9294	$103.93	$103.95	$103.90
Purchase #3	$12.77	13.134%	$14.4472	$14.45	$14.45	$14.40
Purchase #4	$207.46	4.359%	$216.5032	$216.50	$216.50	$216.50
Purchase #5	$16.56	7.848%	$17.8596	$17.86	$17.85	$17.90
Purchase #6	$237.56	7.308%	$254.9209	$254.92	$254.90	$254.90
Purchase #7	$66.61	9.450%	$72.9046	$72.90	$72.90	$72.90
7 purchase totals =	$644.13		$692.9022	$692.90	$692.90	$692.80