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	$131.46	9.304%	$143.691	$143.69	$143.70	$143.70
Purchase #2	$193.77	9.200%	$211.5968	$211.60	$211.60	$211.60
Purchase #3	$138.99	3.449%	$143.7838	$143.78	$143.80	$143.80
Purchase #4	$136.83	3.335%	$141.3933	$141.39	$141.40	$141.40
Purchase #5	$79.51	12.177%	$89.1919	$89.19	$89.20	$89.20
Purchase #6	$29.48	12.284%	$33.1013	$33.10	$33.10	$33.10
Purchase #7	$15.39	3.424%	$15.917	$15.92	$15.90	$15.90
7 purchase totals =	$725.43		$778.6751	$778.67	$778.70	$778.70