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	$127.39	3.802%	$132.2334	$132.23	$132.25	$132.20
Purchase #2	$24.55	11.789%	$27.4442	$27.44	$27.45	$27.40
Purchase #3	$86.40	3.762%	$89.6504	$89.65	$89.65	$89.70
Purchase #4	$90.57	5.813%	$95.8348	$95.83	$95.85	$95.80
Purchase #5	$19.89	5.545%	$20.9929	$20.99	$21.00	$21.00
Purchase #6	$126.35	6.254%	$134.2519	$134.25	$134.25	$134.30
Purchase #7	$106.90	11.767%	$119.4789	$119.48	$119.50	$119.50
7 purchase totals =	$582.05		$619.8865	$619.87	$619.95	$619.90