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	$94.57	13.152%	$107.0078	$107.01	$107.00	$107.00
Purchase #2	$171.72	7.553%	$184.69	$184.69	$184.70	$184.70
Purchase #3	$13.26	12.286%	$14.8891	$14.89	$14.90	$14.90
Purchase #4	$158.82	12.655%	$178.9187	$178.92	$178.90	$178.90
Purchase #5	$117.42	10.109%	$129.29	$129.29	$129.30	$129.30
Purchase #6	$102.67	13.718%	$116.7543	$116.75	$116.75	$116.80
Purchase #7	$78.32	6.632%	$83.5142	$83.51	$83.50	$83.50
7 purchase totals =	$736.78		$815.0641	$815.06	$815.05	$815.10