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	$82.62	7.178%	$88.5505	$88.55	$88.55	$88.60
Purchase #2	$101.89	9.535%	$111.6052	$111.61	$111.60	$111.60
Purchase #3	$101.25	13.831%	$115.2539	$115.25	$115.25	$115.30
Purchase #4	$81.52	7.640%	$87.7481	$87.75	$87.75	$87.70
Purchase #5	$105.70	8.342%	$114.5175	$114.52	$114.50	$114.50
Purchase #6	$101.59	5.590%	$107.2689	$107.27	$107.25	$107.30
Purchase #7	$139.33	7.814%	$150.2172	$150.22	$150.20	$150.20
7 purchase totals =	$713.90		$775.1613	$775.17	$775.10	$775.20