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	$91.42	8.851%	$99.5116	$99.51	$99.50	$99.50
Purchase #2	$250.31	12.105%	$280.61	$280.61	$280.60	$280.60
Purchase #3	$88.78	4.259%	$92.5611	$92.56	$92.55	$92.60
Purchase #4	$119.94	6.394%	$127.609	$127.61	$127.60	$127.60
Purchase #5	$208.30	12.133%	$233.573	$233.57	$233.55	$233.60
Purchase #6	$90.93	7.430%	$97.6861	$97.69	$97.70	$97.70
Purchase #7	$168.81	13.464%	$191.5386	$191.54	$191.55	$191.50
7 purchase totals =	$1,018.49		$1,123.0894	$1,123.09	$1,123.05	$1,123.10