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	$48.91	10.667%	$54.1272	$54.13	$54.15	$54.10
Purchase #2	$24.83	10.858%	$27.526	$27.53	$27.55	$27.50
Purchase #3	$226.61	7.498%	$243.6012	$243.60	$243.60	$243.60
Purchase #4	$109.99	12.435%	$123.6673	$123.67	$123.65	$123.70
Purchase #5	$172.55	10.629%	$190.8903	$190.89	$190.90	$190.90
Purchase #6	$172.59	13.865%	$196.5196	$196.52	$196.50	$196.50
Purchase #7	$32.85	5.291%	$34.5881	$34.59	$34.60	$34.60
7 purchase totals =	$788.33		$870.9197	$870.93	$870.95	$870.90