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	$74.58	11.151%	$82.8964	$82.90	$82.90	$82.90
Purchase #2	$223.69	10.612%	$247.428	$247.43	$247.45	$247.40
Purchase #3	$39.61	4.780%	$41.5034	$41.50	$41.50	$41.50
Purchase #4	$160.75	9.660%	$176.2785	$176.28	$176.30	$176.30
Purchase #5	$69.81	4.452%	$72.9179	$72.92	$72.90	$72.90
Purchase #6	$128.32	3.531%	$132.851	$132.85	$132.85	$132.90
Purchase #7	$79.37	7.845%	$85.5966	$85.60	$85.60	$85.60
7 purchase totals =	$776.13		$839.4718	$839.48	$839.50	$839.50