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	$84.41	5.764%	$89.2754	$89.28	$89.30	$89.30
Purchase #2	$237.63	6.245%	$252.47	$252.47	$252.45	$252.50
Purchase #3	$127.95	11.647%	$142.8523	$142.85	$142.85	$142.90
Purchase #4	$171.63	6.194%	$182.2608	$182.26	$182.25	$182.30
Purchase #5	$146.29	12.342%	$164.3451	$164.35	$164.35	$164.30
Purchase #6	$114.87	3.754%	$119.1822	$119.18	$119.20	$119.20
Purchase #7	$166.50	13.555%	$189.0691	$189.07	$189.05	$189.10
7 purchase totals =	$1,049.28		$1,139.4549	$1,139.46	$1,139.45	$1,139.60