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	$235.39	8.364%	$255.078	$255.08	$255.10	$255.10
Purchase #2	$198.45	4.476%	$207.3326	$207.33	$207.35	$207.30
Purchase #3	$56.56	3.327%	$58.4418	$58.44	$58.45	$58.40
Purchase #4	$187.93	9.223%	$205.2628	$205.26	$205.25	$205.30
Purchase #5	$36.31	12.626%	$40.8945	$40.89	$40.90	$40.90
Purchase #6	$90.44	4.589%	$94.5903	$94.59	$94.60	$94.60
Purchase #7	$146.96	3.355%	$151.8905	$151.89	$151.90	$151.90
7 purchase totals =	$952.04		$1,013.4905	$1,013.48	$1,013.55	$1,013.50