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	$68.67	11.551%	$76.6021	$76.60	$76.60	$76.60
Purchase #2	$128.63	7.688%	$138.5191	$138.52	$138.50	$138.50
Purchase #3	$71.58	6.552%	$76.2699	$76.27	$76.25	$76.30
Purchase #4	$123.40	12.183%	$138.4338	$138.43	$138.45	$138.40
Purchase #5	$35.51	6.466%	$37.8061	$37.81	$37.80	$37.80
Purchase #6	$27.95	13.289%	$31.6643	$31.66	$31.65	$31.70
Purchase #7	$38.59	11.144%	$42.8905	$42.89	$42.90	$42.90
7 purchase totals =	$494.33		$542.1858	$542.18	$542.15	$542.20