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	$27.45	3.269%	$28.3473	$28.35	$28.35	$28.30
Purchase #2	$119.35	12.519%	$134.2914	$134.29	$134.30	$134.30
Purchase #3	$135.28	12.504%	$152.1954	$152.20	$152.20	$152.20
Purchase #4	$187.52	4.866%	$196.6447	$196.64	$196.65	$196.60
Purchase #5	$31.76	3.285%	$32.8033	$32.80	$32.80	$32.80
Purchase #6	$35.58	11.140%	$39.5436	$39.54	$39.55	$39.50
Purchase #7	$95.58	13.696%	$108.6706	$108.67	$108.65	$108.70
7 purchase totals =	$632.52		$692.4963	$692.49	$692.50	$692.40