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	$37.42	5.328%	$39.4137	$39.41	$39.40	$39.40
Purchase #2	$147.38	4.412%	$153.8824	$153.88	$153.90	$153.90
Purchase #3	$114.70	10.274%	$126.4843	$126.48	$126.50	$126.50
Purchase #4	$84.79	5.334%	$89.3127	$89.31	$89.30	$89.30
Purchase #5	$225.73	12.191%	$253.2487	$253.25	$253.25	$253.20
Purchase #6	$250.87	11.445%	$279.5821	$279.58	$279.60	$279.60
Purchase #7	$146.31	11.429%	$163.0318	$163.03	$163.05	$163.00
7 purchase totals =	$1,007.20		$1,104.9557	$1,104.94	$1,105.00	$1,104.90