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	$218.64	4.413%	$228.2886	$228.29	$228.30	$228.30
Purchase #2	$176.97	12.685%	$199.4186	$199.42	$199.40	$199.40
Purchase #3	$81.75	10.188%	$90.0787	$90.08	$90.10	$90.10
Purchase #4	$40.87	6.808%	$43.6524	$43.65	$43.65	$43.70
Purchase #5	$131.90	7.363%	$141.6118	$141.61	$141.60	$141.60
Purchase #6	$31.31	10.237%	$34.5152	$34.52	$34.50	$34.50
Purchase #7	$35.32	11.234%	$39.2878	$39.29	$39.30	$39.30
7 purchase totals =	$716.76		$776.8531	$776.86	$776.85	$776.90