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	$157.30	10.556%	$173.9046	$173.90	$173.90	$173.90
Purchase #2	$69.43	12.588%	$78.1698	$78.17	$78.15	$78.20
Purchase #3	$187.99	11.709%	$210.0017	$210.00	$210.00	$210.00
Purchase #4	$12.30	4.392%	$12.8402	$12.84	$12.85	$12.80
Purchase #5	$56.47	12.473%	$63.5135	$63.51	$63.50	$63.50
Purchase #6	$187.61	11.180%	$208.5848	$208.58	$208.60	$208.60
Purchase #7	$164.46	9.356%	$179.8469	$179.85	$179.85	$179.80
7 purchase totals =	$835.56		$926.8615	$926.85	$926.85	$926.80