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	$132.89	10.182%	$146.4209	$146.42	$146.40	$146.40
Purchase #2	$177.74	8.205%	$192.3236	$192.32	$192.30	$192.30
Purchase #3	$20.71	5.592%	$21.8681	$21.87	$21.85	$21.90
Purchase #4	$249.77	13.616%	$283.7787	$283.78	$283.80	$283.80
Purchase #5	$37.73	10.166%	$41.5656	$41.57	$41.55	$41.60
Purchase #6	$20.93	7.504%	$22.5006	$22.50	$22.50	$22.50
Purchase #7	$180.88	10.827%	$200.4639	$200.46	$200.45	$200.50
7 purchase totals =	$820.65		$908.9214	$908.92	$908.85	$909.00