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	$103.29	6.389%	$109.8892	$109.89	$109.90	$109.90
Purchase #2	$176.85	12.390%	$198.7617	$198.76	$198.75	$198.80
Purchase #3	$37.26	12.194%	$41.8035	$41.80	$41.80	$41.80
Purchase #4	$142.67	3.436%	$147.5721	$147.57	$147.55	$147.60
Purchase #5	$120.88	9.569%	$132.447	$132.45	$132.45	$132.40
Purchase #6	$231.67	9.261%	$253.125	$253.13	$253.15	$253.10
Purchase #7	$109.54	12.330%	$123.0463	$123.05	$123.05	$123.00
7 purchase totals =	$922.16		$1,006.6448	$1,006.65	$1,006.65	$1,006.60