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	$207.90	7.730%	$223.9707	$223.97	$223.95	$224.00
Purchase #2	$38.82	7.340%	$41.6694	$41.67	$41.65	$41.70
Purchase #3	$89.58	12.271%	$100.5724	$100.57	$100.55	$100.60
Purchase #4	$129.90	8.403%	$140.8155	$140.82	$140.80	$140.80
Purchase #5	$44.77	11.611%	$49.9682	$49.97	$49.95	$50.00
Purchase #6	$25.90	9.151%	$28.2701	$28.27	$28.25	$28.30
Purchase #7	$70.87	10.622%	$78.3978	$78.40	$78.40	$78.40
7 purchase totals =	$607.74		$663.6641	$663.67	$663.55	$663.80