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	$133.52	13.325%	$151.3115	$151.31	$151.30	$151.30
Purchase #2	$196.65	3.538%	$203.6075	$203.61	$203.60	$203.60
Purchase #3	$110.96	6.610%	$118.2945	$118.29	$118.30	$118.30
Purchase #4	$35.86	4.813%	$37.5859	$37.59	$37.60	$37.60
Purchase #5	$20.75	4.693%	$21.7238	$21.72	$21.70	$21.70
Purchase #6	$11.27	10.245%	$12.4246	$12.42	$12.40	$12.40
Purchase #7	$36.35	3.639%	$37.6728	$37.67	$37.65	$37.70
7 purchase totals =	$545.36		$582.6206	$582.61	$582.55	$582.60