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	$168.70	10.140%	$185.8062	$185.81	$185.80	$185.80
Purchase #2	$132.64	7.744%	$142.9116	$142.91	$142.90	$142.90
Purchase #3	$94.34	10.786%	$104.5155	$104.52	$104.50	$104.50
Purchase #4	$215.40	3.345%	$222.6051	$222.61	$222.60	$222.60
Purchase #5	$207.35	12.488%	$233.2439	$233.24	$233.25	$233.20
Purchase #6	$112.67	6.310%	$119.7795	$119.78	$119.80	$119.80
Purchase #7	$210.98	5.605%	$222.8054	$222.81	$222.80	$222.80
7 purchase totals =	$1,142.08		$1,231.6672	$1,231.68	$1,231.65	$1,231.60