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	$100.30	10.807%	$111.1394	$111.14	$111.15	$111.10
Purchase #2	$55.78	12.281%	$62.6303	$62.63	$62.65	$62.60
Purchase #3	$137.53	12.151%	$154.2413	$154.24	$154.25	$154.20
Purchase #4	$45.71	11.435%	$50.9369	$50.94	$50.95	$50.90
Purchase #5	$187.51	4.738%	$196.3942	$196.39	$196.40	$196.40
Purchase #6	$205.80	3.194%	$212.3733	$212.37	$212.35	$212.40
Purchase #7	$23.69	6.375%	$25.2002	$25.20	$25.20	$25.20
7 purchase totals =	$756.32		$812.9156	$812.91	$812.95	$812.80