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	$156.89	12.673%	$176.7727	$176.77	$176.75	$176.80
Purchase #2	$122.78	11.411%	$136.7904	$136.79	$136.80	$136.80
Purchase #3	$135.51	11.826%	$151.5354	$151.54	$151.55	$151.50
Purchase #4	$73.77	10.607%	$81.5948	$81.59	$81.60	$81.60
Purchase #5	$103.79	8.647%	$112.7647	$112.76	$112.75	$112.80
Purchase #6	$102.51	9.220%	$111.9614	$111.96	$111.95	$112.00
Purchase #7	$220.80	10.750%	$244.536	$244.54	$244.55	$244.50
7 purchase totals =	$916.05		$1,015.9554	$1,015.95	$1,015.95	$1,016.00