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	$102.64	6.171%	$108.9739	$108.97	$108.95	$109.00
Purchase #2	$179.96	10.774%	$199.3489	$199.35	$199.35	$199.30
Purchase #3	$85.45	13.770%	$97.2165	$97.22	$97.20	$97.20
Purchase #4	$176.54	5.307%	$185.909	$185.91	$185.90	$185.90
Purchase #5	$80.99	10.570%	$89.5506	$89.55	$89.55	$89.60
Purchase #6	$53.40	3.838%	$55.4495	$55.45	$55.45	$55.40
Purchase #7	$40.49	6.307%	$43.0437	$43.04	$43.05	$43.00
7 purchase totals =	$719.47		$779.4921	$779.49	$779.45	$779.40