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	$136.45	12.538%	$153.5581	$153.56	$153.55	$153.60
Purchase #2	$249.51	3.705%	$258.7543	$258.75	$258.75	$258.80
Purchase #3	$151.47	9.372%	$165.6658	$165.67	$165.65	$165.70
Purchase #4	$172.62	4.665%	$180.6727	$180.67	$180.65	$180.70
Purchase #5	$149.31	10.201%	$164.5411	$164.54	$164.55	$164.50
Purchase #6	$99.88	3.202%	$103.0782	$103.08	$103.10	$103.10
Purchase #7	$150.35	9.763%	$165.0287	$165.03	$165.05	$165.00
7 purchase totals =	$1,109.59		$1,191.2989	$1,191.30	$1,191.30	$1,191.40