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	$88.75	3.142%	$91.5385	$91.54	$91.55	$91.50
Purchase #2	$216.77	5.128%	$227.886	$227.89	$227.90	$227.90
Purchase #3	$81.28	10.497%	$89.812	$89.81	$89.80	$89.80
Purchase #4	$128.70	11.304%	$143.2482	$143.25	$143.25	$143.20
Purchase #5	$196.71	11.436%	$219.2058	$219.21	$219.20	$219.20
Purchase #6	$72.53	13.162%	$82.0764	$82.08	$82.10	$82.10
Purchase #7	$132.61	8.726%	$144.1815	$144.18	$144.20	$144.20
7 purchase totals =	$917.35		$997.9484	$997.96	$998.00	$997.90