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	$248.51	8.478%	$269.5787	$269.58	$269.60	$269.60
Purchase #2	$74.58	10.219%	$82.2013	$82.20	$82.20	$82.20
Purchase #3	$82.52	8.847%	$89.8205	$89.82	$89.80	$89.80
Purchase #4	$59.28	3.183%	$61.1669	$61.17	$61.15	$61.20
Purchase #5	$157.78	13.210%	$178.6227	$178.62	$178.60	$178.60
Purchase #6	$75.45	11.202%	$83.9019	$83.90	$83.90	$83.90
Purchase #7	$72.42	8.434%	$78.5279	$78.53	$78.55	$78.50
7 purchase totals =	$770.54		$843.8199	$843.82	$843.80	$843.80