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	$154.87	11.526%	$172.7203	$172.72	$172.70	$172.70
Purchase #2	$202.46	7.440%	$217.523	$217.52	$217.50	$217.50
Purchase #3	$104.85	11.250%	$116.6456	$116.65	$116.65	$116.60
Purchase #4	$95.36	4.495%	$99.6464	$99.65	$99.65	$99.60
Purchase #5	$88.66	3.862%	$92.084	$92.08	$92.10	$92.10
Purchase #6	$100.61	8.595%	$109.2574	$109.26	$109.25	$109.30
Purchase #7	$28.72	11.248%	$31.9504	$31.95	$31.95	$32.00
7 purchase totals =	$775.53		$839.8271	$839.83	$839.80	$839.80