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	$149.46	11.469%	$166.6016	$166.60	$166.60	$166.60
Purchase #2	$226.42	12.114%	$253.8485	$253.85	$253.85	$253.80
Purchase #3	$54.95	8.734%	$59.7493	$59.75	$59.75	$59.70
Purchase #4	$117.95	7.826%	$127.1808	$127.18	$127.20	$127.20
Purchase #5	$176.47	6.329%	$187.6388	$187.64	$187.65	$187.60
Purchase #6	$35.79	11.618%	$39.9481	$39.95	$39.95	$39.90
Purchase #7	$92.67	9.560%	$101.5293	$101.53	$101.55	$101.50
7 purchase totals =	$853.71		$936.4964	$936.50	$936.55	$936.30