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	$166.38	13.306%	$188.5185	$188.52	$188.50	$188.50
Purchase #2	$158.76	6.397%	$168.9159	$168.92	$168.90	$168.90
Purchase #3	$241.85	11.455%	$269.5539	$269.55	$269.55	$269.60
Purchase #4	$24.27	11.476%	$27.0552	$27.06	$27.05	$27.10
Purchase #5	$62.71	6.749%	$66.9423	$66.94	$66.95	$66.90
Purchase #6	$177.74	3.425%	$183.8276	$183.83	$183.85	$183.80
Purchase #7	$66.99	8.276%	$72.5341	$72.53	$72.55	$72.50
7 purchase totals =	$898.70		$977.3475	$977.35	$977.35	$977.30