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	$95.47	5.596%	$100.8125	$100.81	$100.80	$100.80
Purchase #2	$146.64	5.561%	$154.7947	$154.79	$154.80	$154.80
Purchase #3	$38.89	8.582%	$42.2275	$42.23	$42.25	$42.20
Purchase #4	$70.50	3.338%	$72.8533	$72.85	$72.85	$72.90
Purchase #5	$65.53	6.116%	$69.5378	$69.54	$69.55	$69.50
Purchase #6	$164.97	4.240%	$171.9647	$171.96	$171.95	$172.00
Purchase #7	$206.53	11.387%	$230.0476	$230.05	$230.05	$230.00
7 purchase totals =	$788.53		$842.2381	$842.23	$842.25	$842.20