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	$242.29	3.684%	$251.216	$251.22	$251.20	$251.20
Purchase #2	$136.30	4.797%	$142.8383	$142.84	$142.85	$142.80
Purchase #3	$161.53	6.640%	$172.2556	$172.26	$172.25	$172.30
Purchase #4	$41.92	4.493%	$43.8035	$43.80	$43.80	$43.80
Purchase #5	$245.66	4.577%	$256.9039	$256.90	$256.90	$256.90
Purchase #6	$60.89	5.765%	$64.4003	$64.40	$64.40	$64.40
Purchase #7	$166.74	9.713%	$182.9355	$182.94	$182.95	$182.90
7 purchase totals =	$1,055.33		$1,114.3531	$1,114.36	$1,114.35	$1,114.30