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	$82.54	8.445%	$89.5105	$89.51	$89.50	$89.50
Purchase #2	$239.89	13.732%	$272.8317	$272.83	$272.85	$272.80
Purchase #3	$15.96	7.535%	$17.1626	$17.16	$17.15	$17.20
Purchase #4	$62.25	6.508%	$66.3012	$66.30	$66.30	$66.30
Purchase #5	$118.79	3.441%	$122.8776	$122.88	$122.90	$122.90
Purchase #6	$163.50	11.151%	$181.7319	$181.73	$181.75	$181.70
Purchase #7	$40.90	13.469%	$46.4088	$46.41	$46.40	$46.40
7 purchase totals =	$723.83		$796.8243	$796.82	$796.85	$796.80