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	$244.75	13.423%	$277.6028	$277.60	$277.60	$277.60
Purchase #2	$37.27	13.494%	$42.2992	$42.30	$42.30	$42.30
Purchase #3	$111.74	4.618%	$116.9002	$116.90	$116.90	$116.90
Purchase #4	$125.29	9.383%	$137.046	$137.05	$137.05	$137.00
Purchase #5	$21.25	12.373%	$23.8793	$23.88	$23.90	$23.90
Purchase #6	$230.57	12.716%	$259.8893	$259.89	$259.90	$259.90
Purchase #7	$107.54	10.328%	$118.6467	$118.65	$118.65	$118.60
7 purchase totals =	$878.41		$976.2635	$976.27	$976.30	$976.20