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	$71.86	6.423%	$76.4756	$76.48	$76.50	$76.50
Purchase #2	$150.45	5.205%	$158.2809	$158.28	$158.30	$158.30
Purchase #3	$170.57	8.217%	$184.5857	$184.59	$184.60	$184.60
Purchase #4	$127.77	6.656%	$136.2744	$136.27	$136.25	$136.30
Purchase #5	$111.35	7.273%	$119.4485	$119.45	$119.45	$119.40
Purchase #6	$105.47	13.269%	$119.4648	$119.46	$119.45	$119.50
Purchase #7	$121.31	13.367%	$137.5255	$137.53	$137.55	$137.50
7 purchase totals =	$858.78		$932.0554	$932.06	$932.10	$932.10