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	$136.42	7.275%	$146.3446	$146.34	$146.35	$146.30
Purchase #2	$79.67	3.587%	$82.5278	$82.53	$82.55	$82.50
Purchase #3	$179.71	5.212%	$189.0765	$189.08	$189.10	$189.10
Purchase #4	$7.52	4.807%	$7.8815	$7.88	$7.90	$7.90
Purchase #5	$204.42	5.596%	$215.8593	$215.86	$215.85	$215.90
Purchase #6	$244.61	11.861%	$273.6232	$273.62	$273.60	$273.60
Purchase #7	$192.52	13.738%	$218.9684	$218.97	$218.95	$219.00
7 purchase totals =	$1,044.87		$1,134.2813	$1,134.28	$1,134.30	$1,134.30