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	$246.30	13.220%	$278.8609	$278.86	$278.85	$278.90
Purchase #2	$192.60	3.455%	$199.2543	$199.25	$199.25	$199.30
Purchase #3	$106.33	11.455%	$118.5101	$118.51	$118.50	$118.50
Purchase #4	$29.51	10.720%	$32.6735	$32.67	$32.65	$32.70
Purchase #5	$51.77	6.834%	$55.308	$55.31	$55.30	$55.30
Purchase #6	$38.77	10.390%	$42.7982	$42.80	$42.80	$42.80
Purchase #7	$188.58	5.605%	$199.1499	$199.15	$199.15	$199.10
7 purchase totals =	$853.86		$926.5549	$926.55	$926.50	$926.60