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	$39.69	4.571%	$41.5042	$41.50	$41.50	$41.50
Purchase #2	$82.26	9.526%	$90.0961	$90.10	$90.10	$90.10
Purchase #3	$173.78	4.131%	$180.9589	$180.96	$180.95	$181.00
Purchase #4	$214.67	10.239%	$236.6501	$236.65	$236.65	$236.70
Purchase #5	$130.92	9.358%	$143.1715	$143.17	$143.15	$143.20
Purchase #6	$138.85	4.274%	$144.7844	$144.78	$144.80	$144.80
Purchase #7	$33.61	5.410%	$35.4283	$35.43	$35.45	$35.40
7 purchase totals =	$813.78		$872.5935	$872.59	$872.60	$872.70