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	$90.75	11.445%	$101.1363	$101.14	$101.15	$101.10
Purchase #2	$205.28	13.724%	$233.4526	$233.45	$233.45	$233.50
Purchase #3	$75.72	5.705%	$80.0398	$80.04	$80.05	$80.00
Purchase #4	$143.30	3.248%	$147.9544	$147.95	$147.95	$148.00
Purchase #5	$180.26	10.320%	$198.8628	$198.86	$198.85	$198.90
Purchase #6	$40.87	10.199%	$45.0383	$45.04	$45.05	$45.00
Purchase #7	$171.62	11.763%	$191.8077	$191.81	$191.80	$191.80
7 purchase totals =	$907.80		$998.2919	$998.29	$998.30	$998.30