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	$21.60	11.184%	$24.0157	$24.02	$24.00	$24.00
Purchase #2	$208.88	4.731%	$218.7621	$218.76	$218.75	$218.80
Purchase #3	$56.73	7.730%	$61.1152	$61.12	$61.10	$61.10
Purchase #4	$216.77	9.105%	$236.5069	$236.51	$236.50	$236.50
Purchase #5	$126.85	12.206%	$142.3333	$142.33	$142.35	$142.30
Purchase #6	$192.65	8.224%	$208.4935	$208.49	$208.50	$208.50
Purchase #7	$248.32	4.267%	$258.9158	$258.92	$258.90	$258.90
7 purchase totals =	$1,071.80		$1,150.1425	$1,150.15	$1,150.10	$1,150.10