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	$156.36	6.507%	$166.5343	$166.53	$166.55	$166.50
Purchase #2	$118.30	3.201%	$122.0868	$122.09	$122.10	$122.10
Purchase #3	$46.98	11.799%	$52.5232	$52.52	$52.50	$52.50
Purchase #4	$167.71	10.595%	$185.4789	$185.48	$185.50	$185.50
Purchase #5	$139.40	4.590%	$145.7985	$145.80	$145.80	$145.80
Purchase #6	$96.61	13.704%	$109.8494	$109.85	$109.85	$109.80
Purchase #7	$184.86	12.314%	$207.6237	$207.62	$207.60	$207.60
7 purchase totals =	$910.22		$989.8948	$989.89	$989.90	$989.80