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	$111.56	8.172%	$120.6767	$120.68	$120.70	$120.70
Purchase #2	$54.83	12.195%	$61.5165	$61.52	$61.50	$61.50
Purchase #3	$211.31	3.352%	$218.3931	$218.39	$218.40	$218.40
Purchase #4	$91.82	4.592%	$96.0364	$96.04	$96.05	$96.00
Purchase #5	$164.39	9.420%	$179.8755	$179.88	$179.90	$179.90
Purchase #6	$177.47	4.672%	$185.7614	$185.76	$185.75	$185.80
Purchase #7	$35.85	6.750%	$38.2699	$38.27	$38.25	$38.30
7 purchase totals =	$847.23		$900.5295	$900.54	$900.55	$900.60