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	$11.99	5.152%	$12.6077	$12.61	$12.60	$12.60
Purchase #2	$41.33	3.633%	$42.8315	$42.83	$42.85	$42.80
Purchase #3	$124.89	6.182%	$132.6107	$132.61	$132.60	$132.60
Purchase #4	$14.84	13.774%	$16.8841	$16.88	$16.90	$16.90
Purchase #5	$61.81	9.393%	$67.6158	$67.62	$67.60	$67.60
Purchase #6	$85.48	13.717%	$97.2053	$97.21	$97.20	$97.20
Purchase #7	$208.33	3.458%	$215.5341	$215.53	$215.55	$215.50
7 purchase totals =	$548.67		$585.2892	$585.29	$585.30	$585.20