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	$179.49	6.183%	$190.5879	$190.59	$190.60	$190.60
Purchase #2	$134.63	6.175%	$142.9434	$142.94	$142.95	$142.90
Purchase #3	$104.41	8.730%	$113.525	$113.53	$113.55	$113.50
Purchase #4	$87.72	5.480%	$92.5271	$92.53	$92.55	$92.50
Purchase #5	$79.45	4.319%	$82.8814	$82.88	$82.90	$82.90
Purchase #6	$95.99	12.811%	$108.2873	$108.29	$108.30	$108.30
Purchase #7	$197.57	6.304%	$210.0248	$210.02	$210.00	$210.00
7 purchase totals =	$879.26		$940.7769	$940.78	$940.85	$940.70