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	$50.55	9.116%	$55.1581	$55.16	$55.15	$55.20
Purchase #2	$215.83	11.116%	$239.8217	$239.82	$239.80	$239.80
Purchase #3	$95.78	10.159%	$105.5103	$105.51	$105.50	$105.50
Purchase #4	$94.96	12.695%	$107.0152	$107.02	$107.00	$107.00
Purchase #5	$6.41	6.263%	$6.8115	$6.81	$6.80	$6.80
Purchase #6	$162.69	13.278%	$184.292	$184.29	$184.30	$184.30
Purchase #7	$111.93	4.440%	$116.8997	$116.90	$116.90	$116.90
7 purchase totals =	$738.15		$815.5085	$815.51	$815.45	$815.50