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	$220.29	6.416%	$234.4238	$234.42	$234.40	$234.40
Purchase #2	$98.37	9.826%	$108.0358	$108.04	$108.05	$108.00
Purchase #3	$72.89	13.492%	$82.7243	$82.72	$82.70	$82.70
Purchase #4	$132.31	7.206%	$141.8443	$141.84	$141.85	$141.80
Purchase #5	$96.42	9.747%	$105.8181	$105.82	$105.80	$105.80
Purchase #6	$231.51	9.348%	$253.1516	$253.15	$253.15	$253.20
Purchase #7	$82.91	7.827%	$89.3994	$89.40	$89.40	$89.40
7 purchase totals =	$934.70		$1,015.3973	$1,015.39	$1,015.35	$1,015.30