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	$102.28	3.314%	$105.6696	$105.67	$105.65	$105.70
Purchase #2	$238.71	8.456%	$258.8953	$258.90	$258.90	$258.90
Purchase #3	$132.29	9.265%	$144.5467	$144.55	$144.55	$144.50
Purchase #4	$79.84	13.301%	$90.4595	$90.46	$90.45	$90.50
Purchase #5	$86.88	7.584%	$93.469	$93.47	$93.45	$93.50
Purchase #6	$179.91	7.183%	$192.8329	$192.83	$192.85	$192.80
Purchase #7	$77.97	10.723%	$86.3307	$86.33	$86.35	$86.30
7 purchase totals =	$897.88		$972.2037	$972.21	$972.20	$972.20