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	$126.68	12.828%	$142.9305	$142.93	$142.95	$142.90
Purchase #2	$201.50	3.331%	$208.212	$208.21	$208.20	$208.20
Purchase #3	$71.41	9.407%	$78.1275	$78.13	$78.15	$78.10
Purchase #4	$193.93	11.166%	$215.5842	$215.58	$215.60	$215.60
Purchase #5	$54.41	4.231%	$56.7121	$56.71	$56.70	$56.70
Purchase #6	$125.92	13.328%	$142.7026	$142.70	$142.70	$142.70
Purchase #7	$92.78	7.394%	$99.6402	$99.64	$99.65	$99.60
7 purchase totals =	$866.63		$943.9091	$943.90	$943.95	$943.80