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	$142.56	6.342%	$151.6012	$151.60	$151.60	$151.60
Purchase #2	$87.33	13.273%	$98.9213	$98.92	$98.90	$98.90
Purchase #3	$85.35	5.172%	$89.7643	$89.76	$89.75	$89.80
Purchase #4	$236.70	5.726%	$250.2534	$250.25	$250.25	$250.30
Purchase #5	$77.32	3.397%	$79.9466	$79.95	$79.95	$79.90
Purchase #6	$149.80	9.542%	$164.0939	$164.09	$164.10	$164.10
Purchase #7	$35.35	10.808%	$39.1706	$39.17	$39.15	$39.20
7 purchase totals =	$814.41		$873.7513	$873.74	$873.70	$873.80