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	$82.31	9.191%	$89.8751	$89.88	$89.90	$89.90
Purchase #2	$104.42	4.572%	$109.1941	$109.19	$109.20	$109.20
Purchase #3	$203.85	10.282%	$224.8099	$224.81	$224.80	$224.80
Purchase #4	$211.52	6.768%	$225.8357	$225.84	$225.85	$225.80
Purchase #5	$63.61	13.665%	$72.3023	$72.30	$72.30	$72.30
Purchase #6	$50.78	13.420%	$57.5947	$57.59	$57.60	$57.60
Purchase #7	$194.65	10.383%	$214.8605	$214.86	$214.85	$214.90
7 purchase totals =	$911.14		$994.4723	$994.47	$994.50	$994.50