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	$45.92	10.171%	$50.5905	$50.59	$50.60	$50.60
Purchase #2	$80.51	12.151%	$90.2928	$90.29	$90.30	$90.30
Purchase #3	$250.92	7.371%	$269.4153	$269.42	$269.40	$269.40
Purchase #4	$72.85	7.628%	$78.407	$78.41	$78.40	$78.40
Purchase #5	$212.43	12.579%	$239.1516	$239.15	$239.15	$239.20
Purchase #6	$96.69	11.802%	$108.1014	$108.10	$108.10	$108.10
Purchase #7	$246.96	13.635%	$280.633	$280.63	$280.65	$280.60
7 purchase totals =	$1,006.28		$1,116.5916	$1,116.59	$1,116.60	$1,116.60