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	$127.36	13.304%	$144.304	$144.30	$144.30	$144.30
Purchase #2	$103.25	6.469%	$109.9292	$109.93	$109.95	$109.90
Purchase #3	$21.58	13.232%	$24.4355	$24.44	$24.45	$24.40
Purchase #4	$137.29	6.299%	$145.9379	$145.94	$145.95	$145.90
Purchase #5	$152.72	4.267%	$159.2366	$159.24	$159.25	$159.20
Purchase #6	$249.92	3.263%	$258.0749	$258.07	$258.05	$258.10
Purchase #7	$198.45	13.620%	$225.4789	$225.48	$225.50	$225.50
7 purchase totals =	$990.57		$1,067.3970	$1,067.40	$1,067.45	$1,067.30