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	$18.35	4.693%	$19.2112	$19.21	$19.20	$19.20
Purchase #2	$105.34	8.495%	$114.2886	$114.29	$114.30	$114.30
Purchase #3	$138.42	6.525%	$147.4519	$147.45	$147.45	$147.50
Purchase #4	$89.63	8.724%	$97.4493	$97.45	$97.45	$97.40
Purchase #5	$63.61	5.516%	$67.1187	$67.12	$67.10	$67.10
Purchase #6	$94.36	6.564%	$100.5538	$100.55	$100.55	$100.60
Purchase #7	$79.55	3.530%	$82.3581	$82.36	$82.35	$82.40
7 purchase totals =	$589.26		$628.4316	$628.43	$628.40	$628.50