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	$239.92	12.867%	$270.7905	$270.79	$270.80	$270.80
Purchase #2	$16.94	8.165%	$18.3232	$18.32	$18.30	$18.30
Purchase #3	$116.43	13.710%	$132.3926	$132.39	$132.40	$132.40
Purchase #4	$119.61	6.458%	$127.3344	$127.33	$127.35	$127.30
Purchase #5	$42.96	5.520%	$45.3314	$45.33	$45.35	$45.30
Purchase #6	$243.25	13.779%	$276.7674	$276.77	$276.75	$276.80
Purchase #7	$145.29	5.718%	$153.5977	$153.60	$153.60	$153.60
7 purchase totals =	$924.40		$1,024.5372	$1,024.53	$1,024.55	$1,024.50