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	$37.70	4.519%	$39.4037	$39.40	$39.40	$39.40
Purchase #2	$164.29	13.509%	$186.4839	$186.48	$186.50	$186.50
Purchase #3	$58.52	7.145%	$62.7013	$62.70	$62.70	$62.70
Purchase #4	$37.71	11.394%	$42.0067	$42.01	$42.00	$42.00
Purchase #5	$28.31	12.315%	$31.7964	$31.80	$31.80	$31.80
Purchase #6	$65.59	9.172%	$71.6059	$71.61	$71.60	$71.60
Purchase #7	$14.43	4.394%	$15.0641	$15.06	$15.05	$15.10
7 purchase totals =	$406.55		$449.0620	$449.06	$449.05	$449.10