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	$9.85	10.413%	$10.8757	$10.88	$10.90	$10.90
Purchase #2	$13.50	6.498%	$14.3772	$14.38	$14.40	$14.40
Purchase #3	$225.46	6.624%	$240.3945	$240.39	$240.40	$240.40
Purchase #4	$54.40	3.788%	$56.4607	$56.46	$56.45	$56.50
Purchase #5	$80.92	5.266%	$85.1812	$85.18	$85.20	$85.20
Purchase #6	$157.68	4.421%	$164.651	$164.65	$164.65	$164.70
Purchase #7	$75.76	9.409%	$82.8883	$82.89	$82.90	$82.90
7 purchase totals =	$617.57		$654.8286	$654.83	$654.90	$655.00