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	$235.50	9.528%	$257.9384	$257.94	$257.95	$257.90
Purchase #2	$176.79	4.717%	$185.1292	$185.13	$185.15	$185.10
Purchase #3	$157.66	5.424%	$166.2115	$166.21	$166.20	$166.20
Purchase #4	$41.66	4.480%	$43.5264	$43.53	$43.55	$43.50
Purchase #5	$60.60	6.478%	$64.5257	$64.53	$64.55	$64.50
Purchase #6	$10.89	10.493%	$12.0327	$12.03	$12.05	$12.00
Purchase #7	$52.26	13.335%	$59.2289	$59.23	$59.25	$59.20
7 purchase totals =	$735.36		$788.5928	$788.60	$788.70	$788.40