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	$112.87	4.445%	$117.8871	$117.89	$117.90	$117.90
Purchase #2	$199.95	8.713%	$217.3716	$217.37	$217.35	$217.40
Purchase #3	$20.76	7.278%	$22.2709	$22.27	$22.25	$22.30
Purchase #4	$20.69	8.472%	$22.4429	$22.44	$22.45	$22.40
Purchase #5	$132.86	6.342%	$141.286	$141.29	$141.30	$141.30
Purchase #6	$103.80	9.104%	$113.25	$113.25	$113.25	$113.30
Purchase #7	$27.73	13.469%	$31.465	$31.47	$31.45	$31.50
7 purchase totals =	$618.66		$665.9735	$665.98	$665.95	$666.10