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	$52.90	4.570%	$55.3175	$55.32	$55.30	$55.30
Purchase #2	$12.38	6.296%	$13.1594	$13.16	$13.15	$13.20
Purchase #3	$145.47	9.177%	$158.8198	$158.82	$158.80	$158.80
Purchase #4	$113.76	3.585%	$117.8383	$117.84	$117.85	$117.80
Purchase #5	$219.79	3.689%	$227.8981	$227.90	$227.90	$227.90
Purchase #6	$241.89	5.110%	$254.2506	$254.25	$254.25	$254.30
Purchase #7	$219.63	12.202%	$246.4293	$246.43	$246.45	$246.40
7 purchase totals =	$1,005.82		$1,073.7130	$1,073.72	$1,073.70	$1,073.70