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	$126.31	9.128%	$137.8396	$137.84	$137.85	$137.80
Purchase #2	$96.35	12.575%	$108.466	$108.47	$108.45	$108.50
Purchase #3	$38.39	6.223%	$40.779	$40.78	$40.80	$40.80
Purchase #4	$29.85	8.710%	$32.4499	$32.45	$32.45	$32.40
Purchase #5	$53.43	3.185%	$55.1317	$55.13	$55.15	$55.10
Purchase #6	$35.67	3.789%	$37.0215	$37.02	$37.00	$37.00
Purchase #7	$114.43	3.556%	$118.4991	$118.50	$118.50	$118.50
7 purchase totals =	$494.43		$530.1868	$530.19	$530.20	$530.10