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	$201.94	4.408%	$210.8415	$210.84	$210.85	$210.80
Purchase #2	$82.85	9.274%	$90.5335	$90.53	$90.55	$90.50
Purchase #3	$74.34	3.861%	$77.2103	$77.21	$77.20	$77.20
Purchase #4	$62.86	9.116%	$68.5903	$68.59	$68.60	$68.60
Purchase #5	$230.89	10.655%	$255.4913	$255.49	$255.50	$255.50
Purchase #6	$74.78	3.748%	$77.5828	$77.58	$77.60	$77.60
Purchase #7	$187.28	12.400%	$210.5027	$210.50	$210.50	$210.50
7 purchase totals =	$914.94		$990.7524	$990.74	$990.80	$990.70