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	$15.74	11.540%	$17.5564	$17.56	$17.55	$17.60
Purchase #2	$28.35	13.770%	$32.2538	$32.25	$32.25	$32.30
Purchase #3	$43.88	9.617%	$48.0999	$48.10	$48.10	$48.10
Purchase #4	$125.26	13.481%	$142.1463	$142.15	$142.15	$142.10
Purchase #5	$167.38	10.864%	$185.5642	$185.56	$185.55	$185.60
Purchase #6	$185.49	10.198%	$204.4063	$204.41	$204.40	$204.40
Purchase #7	$118.46	8.142%	$128.105	$128.11	$128.10	$128.10
7 purchase totals =	$684.56		$758.1319	$758.14	$758.10	$758.20