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	$21.43	4.799%	$22.4584	$22.46	$22.45	$22.50
Purchase #2	$142.43	6.789%	$152.0996	$152.10	$152.10	$152.10
Purchase #3	$65.92	8.850%	$71.7539	$71.75	$71.75	$71.80
Purchase #4	$147.33	5.834%	$155.9252	$155.93	$155.95	$155.90
Purchase #5	$129.60	10.212%	$142.8348	$142.83	$142.85	$142.80
Purchase #6	$198.71	4.845%	$208.3375	$208.34	$208.35	$208.30
Purchase #7	$193.75	3.682%	$200.8839	$200.88	$200.90	$200.90
7 purchase totals =	$899.17		$954.2933	$954.29	$954.35	$954.30