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	$243.95	13.459%	$276.7832	$276.78	$276.80	$276.80
Purchase #2	$44.97	8.298%	$48.7016	$48.70	$48.70	$48.70
Purchase #3	$157.97	5.328%	$166.3866	$166.39	$166.40	$166.40
Purchase #4	$151.53	11.192%	$168.4892	$168.49	$168.50	$168.50
Purchase #5	$104.29	6.649%	$111.2242	$111.22	$111.20	$111.20
Purchase #6	$38.89	9.790%	$42.6973	$42.70	$42.70	$42.70
Purchase #7	$132.26	10.540%	$146.2002	$146.20	$146.20	$146.20
7 purchase totals =	$873.86		$960.4823	$960.48	$960.50	$960.50