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	$89.70	12.472%	$100.8874	$100.89	$100.90	$100.90
Purchase #2	$13.98	3.834%	$14.516	$14.52	$14.50	$14.50
Purchase #3	$91.59	5.647%	$96.7621	$96.76	$96.75	$96.80
Purchase #4	$141.52	8.215%	$153.1459	$153.15	$153.15	$153.10
Purchase #5	$195.65	10.323%	$215.8469	$215.85	$215.85	$215.80
Purchase #6	$32.95	11.130%	$36.6173	$36.62	$36.60	$36.60
Purchase #7	$9.50	4.111%	$9.8905	$9.89	$9.90	$9.90
7 purchase totals =	$574.89		$627.6661	$627.68	$627.65	$627.60